Interesting question. It appears most on-line sources are just quoting each other regarding Werfel.
https://en.wikipedia.org/wiki/Louis_Werfel
"On December 25, 1943, the State Department sent a telegram informing Adina Werfel that, while returning from conducting a Hanukah service for American soldiers in Casablanca, the small plane carrying her husband had crashed into the Algerian mountains due to limited visibility caused by bad weather. As a young soldier serving in the American army in Oran, Algeria, Donald B. Butler was one of the soldiers who buried Chaplain Louis Werfel in North Africa with a proper Jewish burial." (The crash occurred on 24 December, 1943.)
Aviationarchaeology.com does not have any crashes in Algeria on December 24th.
Now I was able to find the crash of a plane in Algeria on the 24th. A B-25 from the 321st BG, 446th BS crashed into the Lion Mountain just outside of Oran. The five crewmen on board were killed. The plane was apparently trying to get into La Senia airfield in bad weather. The pilot was Irving E Klang. Search for Klang on the following links:
http://57thbombwing.com/321stHistory/321_BG_1943-12.pdf
http://www.warwingsart.com/12thAirForce/3210144.html
At this time the 321st was based in Italy, so this plane had made a flight from Italy to Africa (and possibly to more than one location in North Africa). So suppose it had flown to Casablanca and was flying back to Italy by way of Oran. Did Werfel hitch a ride on it? I found one Werfel reference that said he was trying to get to an airfield (possible in Oran?) to hold another service. There is no mention of Werfel in the 321st reports of the crash, but I wonder if the 321st would have been informed if Werfel was just hitching a ride on their plane. They certainly did not seem to be involved in the crash investigation.
Note also that Donald Butler, one of the men involved with the burial of Werfel was based in Oran. So another clue pointing to the crash occurring at/near Oran.
The distance from Casablanca ( Morocco ) to Oran (Algeria) is 422 miles, which would take quite a while in something like an L-4, so maybe a B-25 would be a more likely plane. (A B-25, however, would not be a "small" plane so perhaps one "strike" against this theory.)
There does not seem to be a serial number recorded for the B-25, so possibly it was a squadron hack.
I find it hard to believe that their were TWO different weather related crashes into mountains in Algeria on 24 December, 1943 and NEITHER one is recorded in the accident files, but a single missing crash..... might be possible.
The five 321st BG men reported killed were:
Bonacich, Matthew G., Sgt, gunner
Carnes, James B., Sgt, engineering (buried in North Africa American Cemetery)
Graham, Robert W., 2Lt, engineering
Henson, Gerald J., 2Lt, co-pilot (buried in North Africa American Cemetery)
Klang, Irving E., 2Lt, pilot (buried in North Africa American Cemetery).