What is involved in a pericardium removal? What happens after?

Depends; why removed. The pericardium is the lining sac that surrounds the heart. If the lining itself is diseased or the sac is filled with fluids with the net result being compromised cardiac function, then removing the pericardium or simply creating a "window", or a drainage outlet that allows fluid to be absorbed by the lung's pleural space, is needed. It then relieves the underlying problem, improving function.
Percardial stripping. Removal of the pericardium is an open surgical procedure. Once done, you should recover well. You don't need your pericardium. It's like your gall bladder or your appendix. If this is being done for constrictive pericarditis, you'll be all better afterwards.