I don't have ALWAYS ON configured on any of my instances as we have a different tool for handling failover.
We also have some 3rd party tools that don't support windows authentication for SQL Server, so we need to have SQL logins enabled. Some of these tools require the sa account (scary, but not a lot I can do about it. They are hard-coded to use sa and explicitly ask for the sa password... these tools end up getting their own Instance as I don't trust them to not screw up other databases on the same instance OR to store the sa password poorly and have it get leaked). So I don't have sa disabled or renamed on all of my instances.
As for renaming the account and disabling it, renaming isn't really required if it is disabled. If a user (hacker) can get into the system enough that they can enable the sa account, they can also look up who is in the sysadmin role and figure out what you renamed it to.
Now, as for that always on operations dashboard error, is your always on configured to be run as SA? Or for that matter, is anything configured to run as sa? Disabling the sa account is a good practice, but disabling the sa account when it is in use is going to be problematic. Having as few users as possible in sysadmin is also best practice, but I wouldn't recommend removing everyone.