An NLI guarantees that the school will carry forward their portion of the agreement for 4 years at Power 5 schools in terms of the scholarship agreement, and 1 year at non Power 5 schools.
There is no guarantee that a kid will be on the Baseball team. Coaches will routinely go to a player and say “we no longer have a spot on the roster for you, we don’t think you’ll ever play here, you should transfer.” 99.99999% of D1 players are going to transfer, they want to play Baseball.
Contractually, a kid could say “no thanks. I’ll just keep my 25% athletic scholarship and 50% academic scholarship you gave me, and just be a student here and not play Baseball.” It just almost never happens.