They generally don't repopulate automatically, and if they did it would be something your client decided to do, not a global Nostr feature.

You have to have at least one relay to use Nostr. Most have roughly half a dozen to a dozen to ensure access to more posts, and more exposure for their own.

Here are some that might be worth checking out:

wss://relay.damus.io

wss://nos.lol

wss://relay.snort.social

wss://nostr1.current.fyi

wss://nostr-pub.wellorder.net

wss://relay.nostr.bg

wss://nostr.mom

wss://relay.plebstr.com

wss://offchain.pub

wss://nostr.bitcoiner.social

wss://spore.ws

wss://nostr21.com

wss://nostr.oxtr.dev

wss://nostr.bongbong.com

wss://relay.primal.net

wss://nostr.zbd.gg

wss://nostr-relay.nokotaro.com

wss://relayable.org

wss://public.relaying.io