The issue with RPing as if someone else is avoiding/abandoning you without having that permission is that it widens the circle of potential complications and kind of forces other PCs to get their own RP complicated OOCly, perhaps without their knowledge that it's an OOC problem.
It's why I would probably oocly let people know that the person hasn't been available and then RP noncommittal stuff in regards to that and steer RP away from discussions about it, but if it was seeming to impact me a great deal to do that, I'd probably get in touch with staff for guidance as to what I can and cannot work out for myself if the other player cannot or will not communicate with me.
Perhaps my point of view is influenced because I've been in a situation where someone's IC partner/tie in dropped off the face of the earth for a bit, and she really really played up the Poor Me aspect. She didn't really tell anyone that she wasn't in contact with him OOC, so we assumed that he was in agreement with some of the zanier things that she would say as to why he wasn't around. None of us asked, but this was like all she wanted to RP about, all of it revolving about how horrible she was taking this abandonment. Our reactions/actions went along as ICly appropriate. When he returned, unexpectedly, she was happy to act as if none of that had happened, and would get really angry about any references to previous RP surrounding her "IC" feelings of abandonment, ect. It was just an awkward situation all around.
I'm reluctant to spread the potential awkward/retcon beyond what it really needs to be, to be honest. So I think noncommittal if you have no contact, and then adherance to the game policy if there is one/checking in with staff if it's important, or being willing to fudge a little that YOUR pc decides to dump his/her sorry ass if you want to move on is preferable to getting a bunch of other people involved ICly.