The conventional answer of is it better to keep Tilmon vs lose Tilmon is definitely yes. But a raw, freshman center in a new, spread uptempo offensive system.... Maybe it's not a huge loss if he does leave?
No, losing Tilmon & replacing with no one is huge. Even if he isn't a bang in his first year, the only way to get to the second year is after the first. Tilmon will help next year, he will help even more the following year. There is no scenario where losing Tilmon is a good thing.