If you clear the cache and loose the patch, you would just be prompted to re-download it the next time you started DKS (as long as the Xbox was online). I have not seen any DKS specific cache clearing methods mentioned.
This should not have any effect on your saved games. The only potential problem would be if you were offline, or otherwise didn't re-download the patch, and tried to load the patched saves in the unpatched game (that could still work, if the patch didn't change the save file format, but you wouldn't be playing in nightmare difficulty mode, etc).
