They would have lost them, just as the United States did... the French culture of those areas was too strong...
Actually, now that I think of it, the UK may be able to hold them, as I recall they didn't get into a situation like the Great Civil War- I mean, the West, the South, the North, and the Northeast of the country all seceding? It's a shock there was enough of the country left to put up a four-year war to try and stop them... (no surprise that they couldn't be stopped) Sorry, I guess this post just turned into a rant about all those "What if US wins GCW and stays united!11!11" threads that are so popular... totally implausible, I say- there's a reason all those regions don't even have a supranational agency between them even today.