Topic branches come and go, generally disappearing after a single pull request. But release branches can have many pull requests before it is EOL'd.

The PR option to delete the source branch has already bitten us multiple times when we merge from release/* into master.

Suggestion: Disable the option to delete the source branch for PRs that come from a branch matching the Release branch prefix declared in the Branching Model.

Also, having an audit message for branch deletion would make recovery faster.