It's going to be funny when the show ends with all of the major characters (including Don) are all still alive. Is it possible Don will end up offing himself though? I mean his life is falling (fallen?) apart but, his life has fallen apart before and he managed to not kill himself then? What's different now? More alone? Tired of always piecing himself backing together?
Don killing himself doesn't seem likely to me at this point... but if you had told me at the beginning of season 6 that Don would have a breakdown and talk about his disturbing childhood during a meeting I would have said you were crazy.
I should also make note of the fact that Weiner has referred to Don as being a survivor specifically in regards to his advice to Peggy about moving on with your life and how that's a survival mechanism, just moving on that is. Obviously that doesn't mean Don can't kill himself, but it gives me doubt that he'll do it.
Who knows maybe Don offing himself is exactly how his story will end and Weiner and co managed to come up with a great execution that really nails it, I hope so because right now Don offing himself seems like an ending I would not like at all. As for Don doing a window check in this episode, it doesn't have to be foreshadowing any sort of suicide (although it could be that), it could simply be the fact he's in a new office and he's just looking to see the change of scenery.