As it says on the tin. What would happen if the plane taking Franco to Spanish Morroco had disappeared into the sea? Would Mola be able to unite the rebels? Would the Army of Africa be anywhere near the military and political force it was IOTL without the Caudillo?
Either Queipo de Llano or Mola would take over as the rebel leader. This could have very bad consequences in the short term -as without Franco screwing around the war could be over by 1937, giving the Nationals two extra years to massacre the opposition.
Should Mola take over, Spain would continue to be a Republic with the tricolor flag, but become a very repressive military dictature with fascist trappings. Whether Mola would be insane enough to throw his lot with the Axis in WWII; or if the military would allow a limited democratization in the 40's, no one knows. Either way, a Molaist Spain could end like a really screwed up place, an European Myanmar.
Should Queipo replace Franco; after the initial years of repression, Spain could have become a constitutional monarchy with a limited democracy -that's what he argued Franco should do after the end of WWII, and got him ostracized. Then again, we're talking about a man who boasted in his propaganda broadcasts about how his men were mass raping republican women and how that was AWESOME; so maybe he'd reinstate democracy after he was sure that no "subversive" elements remained.
Either way, and barring the dystopian possibility of Spain going even more isolated and repressive after WWII, there's the slim chance that democracy would return to Spain a few decades ahead of schedule: Franco's conviction was that the only way to save Spain from what he saw as its "inner demons" was to never stand down from power and to continue ruling with complete control until his death, and after making sure his successor would continue his work. Other rebel leaders, on the other hand, saw their regime as only a temporary measure to restore order.
