That kind:29 would be published to the outbox relay of each person manually.
I think that's better than requiring group managers to agree on a fallback relay before being banned, because
1) they may not do it because everybody is lazy;
2) the fallback relay may pre-ban them;
3) they may choose it at the time they're creating the group and then years will pass and the fallback relay will be offline at the time they're banned from the primary relay.