In general, it's a good idea to backup your saves manually along the game so you could replay the game from any point - it's like a home-made multiple save slots. The saves are located here:
C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegames\58bbd877-836e-4d00-afd6-ff9705fc4e2c\856
(The letters and numbers of the names of two last folders can differ, but I hope you get the idea.

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If you have more then one Ubi game, you will have several 3-digit or 2-digit folders inside Ubisoft saves folder (one with the long name with letters and numbers). You can locate FC4 folder according to the date and time at which the files inside it were created.
Copy the 3-digit folder and paste it in different place. For example, I created set of numbered folders, you can also put a short description in a folder name after the number, like "A16-before_L1". When you want to replay some save, just copy it back to Ubisoft saves folder, overwriting existing 3-digit saves folder.
Just remember that with cloud sync turned on, at the start of the game it will overwrite manually restored saves with later ones stored on the cloud. So if you wanna replay some manually stored saves, you should turn cloud sync off before entering the game. I would turn it off permanently.
I use this method since FC3 and now really don't get how others can play Ubi games without doing the same thing...