They'll shut down servers and close your account with no reason provided outside of demanding you add a phone number. It's happened to me a few times, and I was squeaky clean on there even when compared to the way I talk on HN. Didn't matter whether I provided a phone number. I'm not the only one it's happened to. Anyone with friends on Discord should make sure to write down their contact information in case Discord one day decides that they or their community doesn't exist anymore. But do they delete your data? No, of course they don't... they keep it all to themselves!