Nuke83 - is this the case even if the school commits to the arrangement in writing (i.e., something more than an written offer, such as an executed financial agreement on signing day, even if no NLI is executed on signing day)? On a related note, can a school be bound by a written commitment provided on signing day of a Spring Roster spot?
So we're only talking about P5 schools. To that point, I'm not sure that any of them would execute a financial agreement without also executing an NLI. The NLI process is "owned" and managed by the NCAA and partner schools "agree" to use the NLI process. The financial agreement is separate from the NLI and if the NLI is signed a financial agreement is REQUIRED, but an NLI isn't required (and maybe not even allowed?) if a financial agreement isn't executed.
The NLI actually locks the player and school down (to a degree). Once the NLI is signed, other schools can no longer recruit player, and the player can no longer change schools without NCAA sit out rules applying. The NLI is only signed by players entering a school in his/her first year, so a player who walks on and makes a team as a freshman or later, never signs an NLI. If a player doesn't sign an NLI, other schools can continue to recruit that player, so I doubt a P5 school would offer a signed financial agreement without the NLI commitment accompanying.
Rick is certainly in a far superior position to answer your question than I.
But, assume for sake of argument, a participating P5 school is allowed to provide a financial agreement to a student without executing an NLI. In that case, I suppose it would be a binding agreement, but I don't know how enforceable it would be with the NCAA. Certainly, you could litigate any financial arrangement if it came to that. I suppose a school could write a financial agreement and contract whereby they make it clear the exact amounts that will be paid to a player each year, including $0 in year one, and if a coach were to offer a deal with nothing in year one but loaded in future years, it would be wise to get such an agreement, but I certainly can't speak to the legitimacy of one.
Likewise, to your second question, I suppose a coach could write a contract guaranteeing a roster spot to a player, but I've never heard of such.
As you've probably read in many other posts, even with NLI, financial agreement, P5 4 year guarantee, etc., a coach can make life miserable enough, quickly enough to get any player he wishes to leave on his own accord.