I believe they get listed in “Community Feed” and party is optional.
Many years ago like 50 there was a retirement party for a guy in the next department over (500 people on that floor). He flatly told them he would not go, they threw it anyway !
I had wondered the same thing. Then when I looked at the one I had the question on, the points have slowed down dramatically. Since leaving she’s only gone up 18 points. Although it might conceivably happen, I would say it is unlikely that we’ll have to worry about it.
I wondered about this so I gave it a test a few years ago. It was during a time when I deleted this account and used a new one for about a year.
I noticed Eponymous_Hipster was close to 20k (or maybe 30?). He was a user who was banned. I used my new account to put him over the threshold to see what would happen.