Even if Kojima leaves today, it's not like the planning stages and early development weren't directly influenced by his vision. Only a radical and expensive rewrite and restaffing could erase that and I doubt Konami wants to go that route. I would imagine that they'd mostly leave the staff and direction alone and simply have it finished according to plan. Worst case scenario would probably be a restricted budget, which could directly influence the final quality. Konami is certainly capable of a screw-up like that. I'm looking at you, Suikoden 4.
Hopefully, though, he will have his hand in the game until the end, even if it's on a single-game contractual basis.
Really, though, thinking about Suikoden, too, what the fuck is wrong with Konami?