I really don't see the internet collapsing from him walking away. If it was a legitimate issue it'd be quickly picked up by another party, commercial or otherwise. I'd suggest he does just walk away from it. Even if a lot of money was pushed his way, I'm willing to speculate that he's burned out from all those hours (100/wk?) over the years and now wants to just set things up for a new person, step out, and close the door; been there, done that.
If we ceased having any NTP servers, then there's a more likely internet collapse scenario. The current NTP software seems to have been doing pretty good over the last couple of decades; or is there something that's progressively changing?
I appreciate that the guy has put a lot of work in to it, a lot of us (OSS developers) have and it's a passion more than anything else; if you get money out of it, it's a bonus, but one should never engage in it thinking there'll be any rewards other than seeing that the software itself grows and maybe a little bit of acknowledgement of what you've done. The OSS community can't get all up in arms with disgust when large corps use our software to help them progress, while not all corps give back to all projects, there's still a lot of stuff that is given back, or donated, even when not legally required.
The ethics of earning money off the back of OSS could be debated, but that's a whole different sphere. A lot of us already donate a lot of money already to various OSS projects as a nice feel-good gesture as well as a way to encourage further developments.