I think it all depends on where Kompany sees his career going right now. He's always been ultra competitive and has fought back from injuries so many times - at 32 years old, he isn't really nearing the usual retirement age for a CB, but obviously he's been plagued with a terrible fitness record for years now, so his is not an average situation.
I'd be inclined to say he should stay on a player/coach type contract, the sort of situation that Carrick was in last season at United. I can't see the club just dropping Garcia in at 4th choice at this point, as much as I would like to see it happen. Having Vinnie stick around for another season or so as an experienced head to call on when required whilst someone like Garcia or Sandler develops could be a good arrangement.
That being said, Kompany being the sort of bloke he is, will probably not see his playing career finished and I could see him moving elsewhere for a season or two if he isn't offered an extension. Perhaps a return to somewhere like Anderlecht, who I'm sure would take a punt on him, however, his wife is a manc and his family will be settled here, so I'm not sure whether he will want to uproot them at this stage in his career.