Is there any other way apart from sa to login to a migrated instance where the target environment is in a different domain?
To avoid this, I usually prefer to set up a fresh installation of an instance in the new domain. Then I restore the databases. Then I script proper instance configurations/agents/other things, adapting them to the new domain.
As suggested by @Ronaldo, you can enter in this emergency situation using:
https://docs.microsoft.com/en-us/sql/database-engine/configure-windows/connect-to-sql-server-when-system-administrators-are-locked-out?view=sql-server-2017
Please, take a look at this guide in case of domain change:
https://social.technet.microsoft.com/wiki/contents/articles/24960.migrating-sql-server-to-new-domain.aspx
It's quite old but the general overview is fine.
This guide to regaining access is also fine:
https://www.sqlservercentral.com/articles/regaining-access-to-sql-server-after-changing-the-domain