You can try
./launcher start app
to get the old container running again.
That doesn’t solve the problem but should get your site up again. You shouldn’t need to restore from backup.
/var/discourse is outside of the container, not inside. That template is what builds the stuff in the container, so that’s worth a try.
Also, with as much RAM as you have, I’d switch to 2-container setup so that you can bootstrap without taking your site down.