They can delist a game from the PS store, but I doubt they would make a game unplayable if it's already installed or if you own it physically.
You can doubt that they will, but that’s just hope rather than a legal or technical guarantee.
It's not based on a legal or technical guarantee. But it's based on what Sony did in the past:
P.T. ( https://en.wikipedia.org/wiki/P.T._(video_game) ) was pulled from the PS store. But Sony didn't make it unplayable if it was already installed. In fact, the wikipedia article says:
> After the cancellation, PlayStation 4 consoles with P.T. installed were listed on eBay for over $1,000
But they do require certain firmware updates to play games, at least they did in the PS3 days. If you hadn't updated to that firmware (say, because you didn't want certain features you used like the OtherOS installation to be deleted) your new physical media would not play. I bought Dark Souls on a disc and could not play it on my console.