Where do you get Hirschman graduating in May? He is not scheduled to Graduate in May, he is only a RS Soph and will be a RS Junior next year. Hirschman is one of the least likely to leave.
I will be surprised if Fishback is offered. People are upset with Embree bringing in Dorman (and to a lesser extent Shrock) - well Fishback has about the same pedigree, he wasn't even getting looks from FCS schools and now he is going to the be the Buffs savior???? They (coaches) are not that interested in him. The Buffs are players over the limit at the moment so they don't have room for another very pedestrian QB.
It has been suggested that Nick is close to graduation, much like Webb did in three years. Given he had a Harvard offer, it's believable that he came into CU with credits from AP courses, and he's spent 3 full summers at CU in addition to 6 semesters. Certainly, graduation is a possibility for him. I have no information either way.
He has two to play two, but if he were to transfer to a D1 program, he'd have to sit that first year. Graduation would allow him to transfer without sitting out.