I have hosted a lot of my own services for a couple of years and plan to continue hosting my instance(endlesstalk.org) indefinitely, unless something very major happens.

As others have mentioned I think multiple admins and backups(hard to verify though) are a good sign, but its only indications and you can't really be sure, if a instance will be there forever. I think there needs to be an easy way to migrate accounts and then the instances going down hopefully gives a notice, so you can move your account.

Gonna be difficult to recover accounts from instance going down without a notice I think. You could regularly take a backup of your account, but that is tedious and you will still lose some data.