I can remove the PG_TRY() and use ereport(LOG, ...) + ExitPostmaster if it feels like a safer path for incorporating a bug fix, but note that there is still a risk that the backend will tear down the postmaster. For example, allocating memory for a memory context can fail, or throwing another error inside the backend startup can also fail, so I think that there will be more work to do after this.
Not ExitPostmaster, of course, but some proc_exit call for the backend and returning status code for the postmaster.
