But for how long will it take for them to find another sucker of a mod to do it for free?

Modding, especially on larger subs, is a PITA and takes way more time than most people think. You can always find users who say they will do it but in my experience with across several 1M+ subs most new mods will either drop out or go inactive in 3 weeks or less.

Less popular subs in the 250k user range will sometimes only get 1 or 2 volunteers and sometimes no one at all.

It isn't nearly as easy to replace moderators as you're making it out to be.