I can't even with this. I look at my shelf and see the book where Vampire the Masquerade died. One of the things I most respected about VtM is they said they were going to end the world, and then they actually ended it. Talking about walking back things, they should have walked back this entire idea. Nothing was stopping anybody from running VtM games using Revised set before Gehenna kicked off. Blah.
Perhaps Descent could work Post-Apocalypse and with zombies if your Apocalypse is not Full Scale All Life Must Die or even Civilization has collapsed completely level
Ex: The Television Series Dark Angel and Revolution both had a Technological Apocalypse where a breakdown in High Technology put the world for the most part into a tech-recession dark age. This resulted in huge die-offs due to things like lack of medical attention and such, and of course resource fighting, but would still leave enough humanity to hide behind among the new City and Nation States that rise out of the Ashes of the Information Age world.
Ex: The Steve Jackson Games Car Wars setting is a Dystopic future where wars and some viruses that wiped out Wheat and Rice and the like + Gas shortages followed by a pretty serious but not always lethal plague put the world into a very different state with the United States being a collection of smaller countries and people settling their road rage with pop up turrets and lots of led. The GURPS coverage for that world is easily converted into another setting and has all the fluff -- and could provide a perfectly viable backdrop for a game with Demons and Changelings and Sineaters -- and when the zombies come, the mortal population is pretty much going to respond with the uberviolence they are more than capable of dishing out. Which is kind of awesome.
And of course... the fall of civilization could be a thing that is played through in the game, perhaps the Zombies are just a tool of the God Machine to flush out the Rogue Agents who chose Mankind over obedience. Rogues hide among humans, solution, drive humans into clusters with Dead Humans and have Dead Humans attack the cover of the Rogues until the Rogues reveal themselves. After all, the GM can always make more humans later if it needs to....
As to the mechanics, I can't speak to any of that, I have not immersed myself in that book enough to have an opinion, but, I'd probably side with Coin on matters of not changing it so much that the intended experience of the design can't be met. I would be disappointed if I signed up to play Demon: The Descent and ended up playing something perhaps just as cool, but very different than what I expected.
YMMV
The first game I played on in a MU format (not counting AOL games using Private Chat rooms with names of the location etc) was Anomaly Trek MUX which had a pretty detailed map for the station and some smaller ones for key ships -- and then removed ones for particular planets and a frickin' load up a desc for a place and store it holodeck system I loved. The thing is, I walked that grid to go places, I never @tel'd if I could help it unless it was to Planet Hell where an ST'd adventure was going to be going down. I even avoided just using the home command to go back to my quarters unless I absolutely had to go right now, I'd walk the ring to the turbolift, choose my floor, head down to my quarters and then log out.
The next place was Denver -- and it had a pretty big grid, and it had Car bits I could drive around the grid with. I loved that. I had numerous scenes RPing with someone as we drove around the city from one place to another and then kept right on playing as we got out and went into the Chantry or whatever. Again, I rarely just jumped -- I went through the city unless I was logging on for a scene starting RIGHT NOW being run by someone else.
One of the things I missed on TR was the culture of actually traveling the grid (AND MY CAR). I ended up traveling the grid a lot anyway because it was important to me to know the layout of the City so I could RP better about it. It was good for me to say, Oh yeah, the Tapas bar is here, by this... but if you want the best clock shop, you can go over here by this and check that out.
I like lots of places available for me to go to, it helps inspire RP ideas for me, but I understand the benefit of Temp Rooms, it reminds of the Holodecks on Anomaly. If you only play with a few people in limited areas, a big grid doesn't matter -- but I like open world exploration and a grid full of people's creations give me a chance to discover things ICly and OOCly, and I frankly liked that. Not everyone is looking for the same experience on a MU, obviously, and I can deal with the view that smaller is better and quick travel is king... but I won't lie, if your grid is huge and insanely over built and full of vast amounts of places to go that perhaps see RP in them once a year, I would probably love it because that appeals to my sense of immersion, and for some reason the five to ten minutes it takes to make a temproom and the describe it breaks off my feeling of the flow of RP while in transit, and I like RPing through my world, not just moving from set to set.
@Luna When the "supervision" arrives to find the Llama already dead, stuffed with candy and then made into a Zombie... that isn't supervision. That is damage control. Maybe Collusion. Probably 1/2 of one and 1/2 of the other. 
All you need to be lead astray now is a large selection of corpses and no proximate supervision... or a Llama. That poor innocent Llama.
In my own table top games I let players whose character died (or may as well have -- imprisoned etc) keep all their UNSPENT XP to add to their next character and 1/5 of their earned and spent XP in games where there are no clear levels... like say WoD or GURPS.
In games with a level system -- they get to come in one level lower than the rest of the party/players.
I suppose such a system could work on a MU depending on the XP was awarded. I think some sort of carry over is fair and lets you open potentially new door for character creation. What I personally loath though is Respecs. Even with becomings I'm of the -- take off what you can't have, refund, put on new what you're supposed to have now -- everything else stays school. You may end up with skills/abilities/etc that just don't make sense to your new direction... but that is why its called starting over. Small refund and swapping with the sanctify of merits thing in GMC, I can live with that. "Barry the retainer moved away, but I was lonely so I bought a companion animal from a rescue program." 2 dot Retainer for 2 dot Animal Companion. "I no longer am the best Chef in all the land, but I am a brutal Martial Artist now" Crafts 4 (Cooking) for Brawl 4 (Knucklepunch), no. YMMV
Lt. Dylan Golden, Rapid Response Team Commander -- Star Trek: Anomaly (player)
Fortunae -- Head Writer -- Star Trek Anomaly (wizbit staffer)
Amerigo Hoyle -- Order of Hermes Wizard -- Denver
Brenden Reeve -- Diplomatic Security Service Agent, U.S. Embassy Vienna -- Haunted Memories
Dashiell Bertsch -- Silver Ladder Magus -- The Reach
http://www.amazon.com/His-Majestys-Dragon-Temeraire-Book/dp/0345481283 I enjoyed this series -- its a "realistic" para-historical series set during the Napoleonic Wars era where in addition to ships and cannon and horses and rifles, the nations use Dragons much in the matter of Dirigible and early airplanes were used in WWI. Political intrigue, cultural clashes... and Dragons. I enjoyed it, maybe you will as well.