What should I do about soaked particle board under my kitchen sink?
Remove cabinet door.
Fix leak.
Remove particle board and put a box fan blowing into the cabinet for at least 24 hours. Treat the floor under there with a mold killing cleaning spray. Put the fan back while you cut the new bottom. I would do it piecemeal before removing the face of the cabinet. Which you may have to because removing the face of a corner cabinet will only give you another 2 inches or so. You would have to pull the counter top and remove the top of the cab to get a full piece in there. You may need a support under the planks in the middle somewhere but it beats destroying your kitchen.