Realistically, the rule should be that if a coaching change occurs the LOIs that are in place should immediately be rescinded and the player is immediately a free agent and elligible to look at more schools. Usually these kids are signing with a particular coach and not a school anyway.
Should the rule change? Maybe. Either way, it works to this effect anyways. The NLI clearly states that they are committing to a school not a coach. It can't make it much clearer than how it is stated.
Again though, after a coaching change, they are generally let out of the NLI anyways.