Thomas may well be leaving because he is scheduled to graduate this year but still has a year of eligibility. That makes him a kind of free agent in terms of finding a graduate program that will give him a free ride. And Kennedy, who has been plagued by injuries, is likely leaving to find some playing time. Likely at D2/D3. He would likely have not been in their rotation this year.
As for Watson, I doubt he makes the NBA but he is a very good PG. Likely had a number of POY votes from the coaches. He will get offers from BCS-conference programs, possibly a lot of them if he takes his time.