If this is the dialog you are shown in this case, then there is indeed something we need to do here. We should show a message that relates to what has actually happened. Something like:
Log in
You can’t log in. Your account has been deactivated, and you must reconfirm your email address before you are allowed to log in again.
Send activation email
I’m not surprised if this UX bug hasn’t reared its head because it’s such a rarity for an admin to not log in for a full year on a site that has not been decomissioned.
I also think we should consider removing/hiding the invalidate inactive admin email after days setting - the likelihood that any admin cares about this is very low but I can see the benefit for the ongoing security of a site that admin accounts that are no longer used are deacitvated.