Gerald
Will I still be able to receive mail?
Yes.
Will I still be able to send mail?
Yes.
Will all mail be irreversibly deleted without warning?
No.
Will it randomly revert to 5 community accounts which work and randomly selected additional accounts will stop working?
You fall back to community, that said if you have more than 5 accounts, you will not be able to add new accounts or modify existing accounts, just being able to delete down to 5 (normal) accounts.