1). It would be beneficial to at least get a chance to compare offers before you make a decision, so remaining on the waitlist provides a clear advantageous consequence.
2). Letters of intent aren't a binding contract, and school admissions officers all know that. And if they don't, they're dumb. There's no way reneging on it can come back on you. Therefore, there's no potentially disadvantageous consequence.
Therefore, you should stay on the waitlist, and if your name is called you can evaluate the debt at that time. It might seem somewhat dishonest, but it's the nature of the game: medical schools have no qualms misleading applicants and misrepresenting their intentions (see: Mayo fiasco in the 2017-2018 thread, Columbia 2017-2018 thread).
There is really no point in looking at prestige if you are not interested in going into a competitive specialty or interested in research. Therefore I would put prestige aside and reevaluate based on finances and where you see yourself happiest.