How could the Spanish maintain their claim to all of Hispaniola?
Would a massive Slave revolution occur like it did for the French. Or would the lighter controls that Spanish slaves had be enough to avert such an event.
What would Hispaniola look like in the Modern period?
Have Spain fare better in the War of the Nine Years or whatever you prefer to call it. The French colony would not be legally established, though the already Frenchmen would likely stay. Their colony would not expand though, so that the Island would be overall similar to Spanish part in its entirety, except that a minority of the White settlers would be french-speaking. I don't see the kind of large scale slavery put in place by the French to come up under Spanish rule in anywhere near the extent it did OTL. Hispaniola would probably share the fate of Cuba and Puerto Rico in late 18 and 19 c. If American-Spanish war happens on schedule, its developement would be affected and the final arrangement of it might be different (maybe butterflying things in the Philippines). Probably now Hispaniola is wholly a Spanish-speaking nation, closely linked to the US if not associated to them, unless a Cuba-like revolution happened there at some point. The part what is nowadays Haiti would be overall better of, even of course still struck by earthquakes and hurricanes, would be less poor and less populated, and more mixed. It would lack though its highly glourious past of unbroken chains and military skill, the remarkable honour of having seen the only successful slave revolution in known history, and THIS would have significant consequences in the world either affecting the Revolutionary and Napoleonic wars (IF they happen on schedule) and the general attitudes towards slavery. Probably slavery would be generally more accepted in the West for a little longer. Revolutionary France might not abolish it at all or do it only in limited and gradual manner, only to see it reversed without massive opposition. This alone would change many things in many places.