The real guarantee that Ash will be there is the fact that Rutgers cannot afford another buyout. They have bought out too many contracts recently and they are still in the hole even after their B1G money grab*. Rutgers' AD has to determine whether to let football go until Ash complete his contract or to beg a big donor (of which there are fewer and fewer for the AD). The first confirms Rutger's commitment to big time sports (no commitment, only a money grab) while the second confirms total desperation. Not much of a choice. No money to buy out a contract, let alone bring in a proven coach.
* I know that Rutgers is still not receiving a full share, but the infusion of cash into a system that perpetually loses $25-$35MM and still manages to perpetually lose big money, is not a winning venture. Besides, even the over hyped estimates of $50MM/annually from the B1G's BTN are not quite as accurate as one believes. Even if they were, Rutgers "net" gain would be insignificant compared to other P5 schools that manage their sports revenues even at a near break even level.