Say as a result of the Algerian war, France ends up as a military dictatorship in possession of Algeria.
How would a French military dictatorship effect the EU
Would it encourage the survival of dictatorships in Spain,Portugal, and Greece.
How would this impact Francafrique
Could such a dictatorship survive into the modern day
It depends a lot on the circumstances and timing of such a dictatorship. If the coup is staged as a result of maybe De Gaulle being assassinated by left wing militants and the country slipping towards chaos, the rest of the West will be more amenable to it than if the military takes over as a result of fears over Algerian independence. But even if the former situation happens, the West will expect the military to hold elections of some kind and surrender power back to a civilian government.
I don't know enough about this period in France to say what could lead to the rest of Europe accepting the military being in charge, and it'd doubtlessly affect the development of the EU, more so the earlier it happens. One scenario I often go back to when dealing with France in this period is an Italy that stays neutral during WW2 and carves a stronger, Mediterranean oriented, third path for itself and the other Southern European states during the Cold War. If France under this hypothetical military dictatorship is friendly to Italy, the balance of power on the continent could swing definitively to this bloc. The US would keep its presence in Germany for obvious reasons, but the rest of Europe would be a lot more independent of Washington's influence, barring maybe the UK, who'd see the developments on the continent as a reason to develop relationships with the US and ANZAC countries.
France's role in Africa would probably be more extensive than OTL, maybe looking more like it does today, except decades early. Regimes friendly to French interests are more actively supported whereas OTL they were passively so. The Ivory Coast is an example that comes to mind. I don't recall many of the finer details, but French support, or the lack thereof, was critical in the power games at several points in the country. That factor would only be strengthened ITTL.
As for it lasting to the modern day, I don't see it. Short of the military reinstalling the monarchy and using the King to eventually mediate a sort of power handover while allowing the military to keep a lot of control a la Thailand, the dictatorship is on a timer as soon as it starts. But it would help the regimes in Spain and Portugal, and thus indirectly the events in those countries overseas territories. Instead of being paranoid about FDI as he was OTL, perhaps Salazar in Portugal would be more open to money coming from an ideologically friendly France.
Hopefully that covers all the bases, I realize I jumped around a lot.