I know if I was a professional athlete, I'd rather retire at close to the top of my game (in my waning years) than wait until my body gives out or I take a huge dip in production.
We probably won't be making it to the playoffs next year and the season following that will largely depend on our RFA/youth success (or failures), so the team will most likely not make it to the playoffs while Doan is healthy enough to play consistently.
Of course, he may still be having fun and feeling healthy, so he could stick around. I doubt he'd sign elsewhere. He's had a long career and deserves some time off while he is still largely healthy.
In brief, I could easily see him retiring after this season despite the fact that he might have a few more decent seasons in him