Actually it already happened to me when playing at Yucata more than once.
If Quebec is fortified, Brits may choose to siege Trois Rivieres, which is usually weak. After losing it, all of the following cities are lost because they don´t have a connection with Quebec anymore, a player may not use their cards to anything. France may still have Tadoussac and Montreal with a boat on their cards to try to get TR back asap. That means if they are still owned, of course, because if the player had lost them too, there is not a single way to recover and rebuild the colonies anymore, since the bateaux card was removed from the deck. It becomes a dead end (literally?). I could not find a reason (thematic or not) to this card be removed from the game. When I play face to face, it remains on the empire deck. (I am glad I have the first edition).