A multi-million dollar fund is not needed at all. There is a simple solution: to have the guts to do what’s right and fire the underperforming rebbis.
What do you mean they have no place else to go? Surely Hashem will provide for their livelihood somehow. There are hundreds of schools to apply for other teaching positions, and there are hundreds of other potential jobs that do not require a college degree.
Maybe Hashem’s plan is that a rebbi is fired and then goes into business and is known mainly for his tzedakah rather than his contributions to chinuch? Maybe he will then become independently wealthy and become a full-time learner? Everything Hashem does is for the best, even going into a line of work that one is not suited for and having to switch careers at midlife.