We faced a similar dilemma with our 2020 RHP, when he lost a year to testicular cancer. He wasn't a P5 prospect, but he was on a path to the mid-majors before he was diagnosed. Fortunately, earlier this fall the right school came through with an offer, but only because they had another pitching commit fall out.
So we had looked closely at doing a post-grad year and in the process we found some things about IMG Academy that might make it worth a look. It's crazy expensive, but it offers some advantages, including high visibility with the big college programs. Their PG players take classes through the University of South Florida, so when you leave you've got freshman English and some other classes in the bank, credits you don't have to pay for when you get to your four-year school. And finally, they require a sizable deposit, but they told me I'd get nearly all of it back if our son enrolled in an NCAA institution. So, it's possible to reserve a spot in a PG program and continue the recruiting process without a lot of risk.
As many folks have already said, the recruiting window for pitchers never closes completely. The options may be fewer later, but you never know.
In the mean time, good luck and best to your son as he recovers.