I think that the end for Thompson, when it comes, will come suddenly. His performances last year were fine - and for the first time in several seasons he stayed relatively injury free (though he started the season on the injury list). How long he can maintain that is the question...There is no question Thommo's days are numbered you are dead right he will need to be moved on and thinking he will remain in the mid is probably a bit more of hope than a certainty, look at Judd for the past couple of years one of the best midfielders ever yet he struggled at his age.
The problem with Thompson is that he doesn't have any other strings to his bow. He doesn't have the flexibility, that Roo had, of going forward as a medium marking option. For Thompson, it's midfield or nothing. If he stops being able to perform in the middle, then it's game over.
My big concern is that we have a distinct lack of quality options to replace him once he's gone. But we've had that debate already, and I don't particularly want to revisit that argument again right now.
I think 2016 will be Thompson's last season. Whether he makes it all the way through to the end, while still performing strongly, that's what I'm uncertain about.