To answer your questions:
1. Academic scholarships tend to be based more on ACT/SAT test scores, yet they are also combined with the student GPA. For a NCAA DII school, a half athletic scholarship is a good offer. I would expect that if your daughter tests well, and combined with the gpa, she should have a very good total package. The majority of admissions offices will have some type of a listing or matrix about the academic scholarship opportunities and amounts, as they relate to test scores/gpa.
2. The National Letter of Intent is the legal contract between athlete and the school. The NLI will be honored by a new coach because the contract is with the school. The coach can easily change their mind about an incoming player, but financially/scholarship wise, they could not act upon this decision until after the first year.
3. The NLI is just a one year contract - Remember that the NLI and scholarship are two separate issues. The NLI is just for the first year of an athlete attending the school; it is just the ensure the first year is honored. Schools will send separate scholarship papers to capture the various scholarship avenues. After that initial year, the NLI leaves and the next year is up to the school/athlete.
4. It is basically too late for Plan B, as she is going to be a Senior in 2014. If the coach was going to get fired, it would have happened last spring - She will sign the NLI before the coach could be fired after next season.
Your question clearly reinforces the need for VolleyFamilies to go through the process of asking a bunch of questions and to make sure a school's academic/social status takes priority.