Considering the difficulties involved in actually getting out of a furball in the WWI arena, not to mention the challenge of just handling the aircraft in general, if he was able to successfully limp away from any bad guys in range with that sort of damage he's EARNED a no-kill ditch.
I would agree with a caveat.
There should be a trench line between each set of fields.
If you get back across to your side of the trenches, you get a ditch.
If you go down on their side, its a kill/capture.
IMHO,
Wab