I moderate a community from a dead instance and want to leave the community I moderate. But when I go to Settings > Moderator, I don't see an option to leave.

Generally you just have to stop giving a shit

Are you the community owner? If not, then you might have to ask them to remove you.

If they're inactive, then you'd want to contact an admin.

I didn't create the community, but I have the ability to remove myself as the owner. But doing so only removes me as owner, not as moderator.

Ah, maybe you have to do it in reverse order, then. It assumed you wanted to stop being owner but still be mod.

I'd go for the admin, then!

Contacting admin is better. So we can lock communities or seek new mods, it will reduce our moderation work.

As @JohnnyEnzyme@piefed.social already told you, you should contact the admin. Doing so you inform them that your community will be unmodcrated.

You can also lock the community so only mod can post there.

Lastly you can post a message in your community and ask for users if they are interested in becoming mod. And then name them as owner.

that's an incredible amount of pointless friction when just not giving a shit anymore is instant, so i'd just rather do the latter. why don't the admins just immediately get pinged when a community's last mod leaves? what happens if the last mod dies and can't contact an admin themselves?

that’s an incredible amount of pointless friction when just not giving a shit anymore is instant

That's what keep the fediverse safe, so we should inform them.

why don’t the admins just immediately get pinged when a community’s last mod leaves? what happens if the last mod dies and can’t contact an admin themselves?

Those are very good questions.

I don't recall well but i think piefed has a feature that can adress this issue. Maybe i'm wrong but it detects mod activities (connexion). And tell admins if it is unmoderated. But i'm not sure.