check your settings in the Uplay Client
if you have Enable Cloud Save Synchronization for supported games checked yes your progress in your game is saved to the cloud
when you start your game after your WIN 10 clean install it should sync or give you the option to use the cloud save
and a tip make sure you set the Uplay Client as Run as Administrator with Windows 10 for best results (i run win 10 pro 64 bit )
( do the same for the Steam Client if you have the Steam version of the title )
also if you do not wanna rely on the cloud save you can manually back up your saved game
just copy the right folder over on to a USB thumb drive and when you reinstall your OS and u play again copy the file right back to its original location
i do it all the time and made backed up saves for every level of the game + every level of the valley of the Yeti Campaign
here is a short video of how to create multiple saves by 04AM
https://www.youtube.com/watch?v=E8cTOvbgyrs
now granted he is just making backups of his position in the game .. me i did it a bit differently and created a folder names after each mission then copied my save files in as i went
so i have a folder named Payback on the thumb drive in that folder is a sub folder 856 thats the save from the payback mission
i have a folder named dont_look_down on the thumb drive in that folder is a sub folder 856 thats the save from the dont look down mission
i have a folder named Burn_it_Down on the thumb drive in that folder is a sub folder 856 thats the save from the Burn it down mission
(its 856 because i have the Steam version of the game for the u play only version the folder name is 420 ) dunno why its different .. just know it is
steam uses Program files X 86 / Ubisoft /Ubisoft game launcher / saved games *series of numbers and letters varies between systems * / 856
Uplay only version uses
Program files X 86 / Ubisoft /Ubisoft game launcher / saved games *series of numbers and letters varies between systems * / 420
to replay em i just copy them right back in the Program files X 86 / Ubisoft /Ubisoft game launcher / saved games *series of numbers and letters varies between systems * / folder
to back up a mission i just alt tab out of the game to copy the save to the thumb drive
i keep my backed up saves on a USB thumb drive so i can transfer them over to my laptop or other PC or just replay a level i liked and try a different load out that better suits the mission
to do it this way tho you have to shut off the cloud save sync other wise it will overwrite your saved position with the one from the cloud
GOOD LUCK !