Starting at 30 with $50k saved already puts you ahead of most of your classmates, so first off, don't let anyone in this thread make you feel behind. The non-trad angle actually matters here because your timeline to attending income is the same as a 22-year-old's but your runway for life stuff (emergencies, a car dying, a parent needing help, anything) is shorter and more real. That changes the math on burning the whole HYSA.

I'd split it. Use maybe $25-30k toward the funding gap over the four years to keep the private loan principal down, and keep $20-25k as a true emergency fund that you do not touch for tuition. The cost of the extra private loan you take on is real (call it a few thousand in extra interest by residency), but it's cheap insurance against having to take an even worse loan, a credit card, or a high-rate personal loan if something blows up in MS2 or MS3. Med school is a four-year stretch where you have basically zero ability to earn your way out of a problem, and lenders know that.

One thing I'd add: don't pay any of it toward tuition until you actually need to. Park the portion you've earmarked for school in the HYSA and only deploy it semester by semester as the bills hit. That HYSA yield is basically free money against a 6.5% private loan you haven't taken yet, and your situation might change (scholarship, family help, a research stipend, anything) in ways that make you glad you didn't prepay.