Those bolt holes don't carry any oil. The bolt has a shoulder and a rubber washer. You'll just have some oil leak out when running. Will make a mess but that's all. If you're already bottomed on the washer, no amount of tightening it will change anything and, as you found out, you can break the bolt.
You have to remove the valve cover and you'll probably be able to get the broken bolt out. Change all the rubber washers while you're in there. $500-700 to fix this is insane.