As for random volunteers disappearing, the protection against that is easy - increase the bus factor, by multiple people having necessary access, and by keeping your infrastructure documented. This should be table stakes for any project that becomes even marginally popular.

Then, if a random volunteer disappears, things might slow down due to lack of manpower, sure, but not come to a screeching halt.

You can't increase bus factor with Discord, since it's out of your control.