Almost everyone in Algeria lives in that coastal strip. The portion south of the Atlas Mountains is empty waste populated by nomadic berbers. It will never be a country of its own. So if it isn't owned by the people on the coast, it's going to become past of some other country.
So if there is any end to the Algerian War that keeps part of Algeria for France, the division is not going to be coast vs desert. It's going to be a very small portion of the coast with the rest of the coastal area becoming Algeria. Ostensibly, it would be based around 1-2 major cities with a significant French presence. I think the pied-noirs had slightly over 10% of the population, so that is about how much of coastal Algeria we might expect them to have. Maybe based around Oran?
I think that is an unlikely scenario. If the FLN knows it can get 90% of Algeria, it's likely to keep fighting for the entire area. If France is powerful enough to guarantee it can hold onto a portion of Algeria, why not keep fighting as well to break resistance and keep everything? I don't think it's a compromise that makes sense in practice. There is no one area that one can say is predominantly French, so any division would be arbitrary.
Besides, any continuing French area would be subject to continued terrorist attacks and require substantial defenses. It would be a besieged outpost constantly harassed.
