Almost everything is held server-side, very little is stored client-side. This has been confirmed in discord, and also is easily identifiable if you try and play the game without your network connection turned on.
If you delete your game and files and re-download, as Brent has done once, you don't lose progress, you pretty much just have to re-accept the EULA, and re-play the missions to be able to play antagonist on them.
