Ten years is...pretty much nothing to a Time Lord, so the Master will likely be very similar to how he is at the moment. He'll look exactly the same, at the very least. Difference-wise, let's see. Likely, he'll be a little more...domesticated by then. His mental stability will still be something that comes and goes, though; in general, he'll be decently behaved. Happily married to the Doctor by then, certainly. And knowing the Doctor and his affinity for strays, probably with a goddamn petting zoo attached to the house. :|

other than that I'm not sure so PLOT WITH ME :DDDD