Hypothetically, let's say you have 50,000 in a group (I've seen far bigger on Telegram). All of a sudden, your relay is targeted.

1. How do you communicate to your 50k where to find your new relay?
2. How do you keep your new relay from being immediately targeted by the same actor who took down the first? 

 1) The group members are npubs. Write a note. Tag them from the new group. DM them. Whatever. Groups have a membership list event.

2) It's a server. Put it on a different machine. Protect the machine better. Protect the relay better. Have a fallback mirror.