I think engine failure might have been low down on a pilots list of things to worry about. Several WW1 aircraft had a history of structural failure in flight, The Albatross DV had a lower wing failure problem that was never solved, the Fokker DrI had several upper wing failures in the early models, Lothar Richthofen was lucky to survive after a upper wing failed in his DrI.
Some Nieuports like to shed their wing fabric, these are faults that would usually result in a pilot's death.
Then once combat was entered most single seaters had the gas tank right in front of the pilot, except the Sopwith Camel. It was right behind the pilot, i'll bet that was a comfort.
At least if a engine failed, if it wasn't a catastrophic failure that resulted in a engine fire, a pilot had a good chance of making a controlled landing.