What a crappy situation for the OP's son and teammates.
My 2020's school has not (yet?) asked any signees to "un-sign". It is an underfunded low D1 though, so I'm not sure if those dynamics matter... meaning, pulling what little scholarships they offered won't make much bottom line difference anyway I suppose (especially when considering those tuition dollars would leave once unsigned). Seems this scenario where schools ask 2020s to de-commit this late would only be at fully funded programs and likely lower tuition/non-privates?
As for publicity, in Texas, I know of one D1 that has had a couple (or more?) 2020s de-commit after signing in November. That school had shown some prior recruiting interest in my 2020 until he blew a save in an outing they traveled to watch him pitch back in 2018... looking back, maybe it is better to be (un)lucky than good as I am sure he would have been asked to un-sign, too.