A while back I mentioned that I was considering modifying LogJam to add persistent templates for posts. It since occurred to me that there’s a very much simpler way to achieve the same result: Add a preference option to keep saved drafts after posting, which suppresses the “Delete this draft from disk?” prompt and action. Enabling “Keep saved drafts after posting” de facto turns the drafts list into a list of saved persistent templates. (They can still be deleted if desired from the ‘Open Draft’ dialog, so no functionality is lost by turning this preference on.)
A patch against Logjam 4.5.3 to implement this feature can be found here.