There are those that will stay on Discord because the benefits of the first three outweigh the degradation of privacy. Then there are those that will leave because the first three aren't important enough to outweigh the privacy loss. There will be all sorts of people in between.
HN has a rather amplified showing of folks who won't trust anything unless it's completely decentralized using E2EE clients verifiably compiled from source that they'be personally audited running on hardware made from self-mined rare metals. The reality is that there is a spectrum of folks out there all with different preferences and while some folks will leave (in this case) Discord, others will remain because thats where the folks they want to chat/game/voice with.
Back when I played games one friend in our group was banned from LoL arbitrarily so the whole group switched to Dota 2.
Honestly, all of these are documented probabilities at this point. SNS owners can do very decent predictions on what will happen if they introduce certain kind of friction. Also, it’s not 2005 anymore, people are used to upload their IDs everywhere. I mentioned it before as well, if you’ve used any large app, the chances are you’ve uploaded your ID (AirBnB, Tinder, and etc.)