Yep, keep a copy of the original files, and keep them for some time because you will need to play a bit the game to verify that everything is working and loading fine, if the game is divided in "chapters" or "levels" you should play at least 2 of them to see if the cinematic sequences in between them loads fine, also to see if the files from the second chapter loads fine
And btw... i guess whoever that made this originally released xdelta patches for all the files (not only for the big one), if not somebody should create the others xdelta and make a pack with them
The reason to distribute the patches in xdelta format (only) is because xdelta only stores the changes, and this changes cant be copyrighted
In other words... if you distribute the xdelta patches you can post them in any website, forum or wherever you want, because are legal