Availability groups and Linked Servers
Are linked servers in any way required by availability groups?


Absolutely not needed by SQL Server for Availability Groups!


  Anything wrong with just doing normal due diligence and changing the linked server user to use non-sa and also changing the sa password?


No, I agree with your approach as long as it doesn't break the business requirements. However, if the developers are using it to query around then I could argue that they should be changing their software to do this, rather than a linked server.

I would tend to agree that it's most likely used to automagically sync logins and jobs, but again there is no need for an actual linked server to do this though I could see why they would use a highly privileged account so they wouldn't have to worry about permissions.