I don't know if PR1CE announced he was leaving in advance, if he did I might have missed it. I think he did post a goodbye message.
I have made a lot of tribute memes over the years, after users I like a lot have deleted their accounts. Here is one of them:
imgflip.com/i/3chovn
If users mention they are thinking about deleting and I've had a lot of positive interactions with them, I usually try to talk them out of deleting. I tried to talk RayCat out of deleting his account.
The Terms of Use has a good sentence that sums up the rest. "You can stop using our Services at any time, although we’ll be sorry to see you go."