From the description of the location it is one of the 2 directly around the oil pump main output where the O-ring is.
This is the worst case.
What I would do is remove the pump. clean the area well. using leather or fiberblanket, make a protective layer over the oil pump cavity and make sure to block off the suction pipe and the output hole.
using a mig welder w/ co2 argon mix......place a washer over the broken bolt. make a quick spot weld in the center. might take 2 qick zaps to build up the tack. Then place a nut onto the washer, and repeat to attach nut to washer and bolt head. LET IT COOL!!! after 7~8 mins, remove by turning nut with wrench.
I defintely would not just run it like that. Recipe for disaster, main oil pressure loss.
Actually, yeah, you're right. Crap. I didn't even think of that for some reason. Thank you for pointing that out, because I never would have seen that.
There are two more problems with this, though-
1- The bolt is long gone by this point. It's just the back end of the extractor now.
2- I don't own any welding equipment and, for reasons I can't really get into, I can not be even remotely close to welding equipment.
That being said, I think I've more or less resigned myself to the fact that I'm going to need to look into getting a new block soon. I was planning on actually buying an engine to rebuild just to have around, so maybe this is the reason I needed to do that. This particular engine is already in pretty rough shape, so if this is what does it in, then at least I know what happened.
Meanwhile, I have a '95 EJ22 with over 200k miles on the clock rusting out with a giant hole between the IAC valve and block and it chugs along like a tank. Funny how some things go.