Sorry for your loss. It seems we never have as much time to tell what we know as we think we will.
It is a handsome old gun, and it is OLD, that type of foreend lever goes way back. Likely pre-WW I manufacture, although I would bet it is WW II Occupation loot. Triebel was just one of many small gunmakers in Europe of the day.
There is still a Triebel in business in Germany, although in Berlin, not Augsburg. No way of knowing it if is the same or successor company or another Triebel altogether. But they do trace the family back in gunsmithing for 250 years. For your interest
http://www.triebel.de/