No battle over British airfields or bombing England itself, except maybe occasional attacks against shipping ports. That would be as far as they venture into England. Crank out the U-Boats and send submarines and the entire luftwaffe after commercial shipping. Could the Luftwaffe have added anything to the U-boat campaign by serving as visibility, attacking submarine destroyers to aid U-Boat escape, and bombing commercial shipping itself? Who would win that long, protracted starve them of resources campaign if Germany did not invaded Russia?