However the heck they want to spend it. These are donations. If the guy has been working so hard just to make the world a better place and he wants to disappear with the money, I'd be bummed and I imagine lots of other people would too, but they were donations. A "thank you for busting your back for so long", not a "hey, now you've made it to the big leagues, better saddle up (the way I want you to, by the way)."
We've been using this software (probably worth many millions a year in the private sector) for free for how long? At least for libgcrypt, the initial commit was November 8, 1997. 17+ years ago.
That said, what are the chances this awesome, passionate developer is going to deliberately drop this project he's poured blood, sweat, and probably some tears into? What are the chances that he doesn't labor over the decision on how to spend the money, and consult his peers?
I sincerely hope this doesn't turn into some donation-gate fiasco where everybody's miffed about how the money that was freely donated got spent. This guy has changed the world and deserves to take the money as thanks and not added responsibility. He's already been shouldering that responsibility for years.