To globally delete all automation press ctrl + A to select all, then select Edit-->Delete special. Uncheck everything except automation and click on okay.
The PC can be reset easily. Ctrl + A to select all again, hold down the ctrl key and load the "Misc-Full reset" preset into one of the tracks.
The FX bin you'll need to do one at a time.
I always save a tracking finished version and then mixes after that so I've always got a starting point to go back to.