systemd should be able to start it back up, but you’d lose the ability to shutdown Sonarr from the UI. More info in this thread:
If Sonarr isn’t started in the 5 seconds it should log Starting NzbDrone
as an information log message and then start up. To troubleshoot further you’ll need to enable ((debug logging)) and look at the logs when an update is started to get the update command, if the update fails you’ll want to start Sonarr up again and get the process ID for it then use that new ID in place of the old one and try running the update manually. Probably quickest to switch to the develop branch and test it as there is already a build available and they are much more frequent.