So the founder is going to work at a company they want to work at, and I’m guessing as part of the hiring agreement he had to wind down his activities on or shut down the project…

For his sake I hope he doesn’t end up regretting it when the job isn’t as rewarding as he thought, or he gets laid off after a few months and doesn’t have a project to go back to.

I don’t have enough context to really judge I am sure, but this is a story that happens often enough for me to already think he’s making a massive mistake.

I don't think this is the full story. 99% sure there's either a brand acquisition or tech licensing of some sort involved that he's not allowed to talk about...

Hm... Why not to sell it or give to the community, if there is no intension in further work on the project?

Nothing in the explanation said no further work on the project was intended. It said the online service will go down, and they are joining a larger company. Could very well be that the acquisition of the codebase is part of the deal, and it will be integrated into the products of the new employer. In short, an acquihire.

My first thought was the same. Someone in HN would probably love to buy it and solo run it.