Hi Mark,
I looked at this in Pro 2.7 using a SQL Server 2016 geodatabase and removing or adding a domain to a field is reflected in the Domain Usage pane immediately without having to close and re-open the pane.
I did see that if I actually renamed a domain while the Domain Usage pane was open, it was necessary to click the Domain Usage button on the ribbon after saving the updated domain name in order to refresh and reflect the updated domain name in the pane.
I'd say that the best thing to do would be to test in Pro 2.7, but since you said you're on SQL Server 2014, it doesn't look like that is supported (https://desktop.arcgis.com/en/system-requirements/latest/database-requirements-sqlserver.htm
So I don't think we could have confidence in any results... Are you planning to upgrade your SQL Server version soon?