Since the bug table stores the version name in the bug record rather than link to it, hence, deleting the version from the product versions shouldn't be a problem. The only problem that you will have with the current code is when you get to update an old bug that was associated with this version, in this case Mantis will select a different version from the list. The workaround for that is to populate the list in case of "Update Bug" with the list of versions for the project + the current version (if it is not already in the list).

bug_update_page / bug_update_advanced_page:
With the fields that are populated with a drop-down list, we should consider always filling them from the database + the current value (if it no longer exists), this will allow bugs to maintain their current state when being updated.

With the current DB schema in v1.1.1 it looks straight forward to add a new column to the mantis_project_version_table titled obsolete which is just a boolean. From the manage_proj_ver_edit_page.php a checkbox would need to be added to allow a manager/admin to mark that version as obsolete. Once a version is marked obsolete the bug_report_page.php/bug_report_advanced_page.php pages would need to only pull versions from the database that are not marked as obsolete.

This approach never deletes a version but merely marks it as no longer supported.

Fixed by svn:5127
http://mantisbt.svn.sourceforge.net/mantisbt/?rev=5127&view=rev

Some details of the fix:

1. Added an 'obsolete' logical column to version table.
2. Added the corresponding column to the manage edit page summary view of versions.
3. Added a check box to version edit page.
4. Report Page, Roadmap, Changelog only show non-obsolete versions.
5. Update page doesn't display obsolete version, unless it is the current value set on the bug.
6. Filtering drop downs don't include obsolete versions.