There are no oil passages there......it is broken at the left center case halve between the crankcase where the flywheel and rotor spins.....and the rear pulley.  And it doesn't appear the broken piece has gone anywhere....there is a tab of aluminum in the photo that is broken and shoved forward a bit.  It might be worth removing the cover and see if you can shove that aluminum back into place before applying the JB weld.

The photo shows the break is right at the seam between the left half of the crankcase and the left side cover.....so unfortunately just replacing the cover and gasket is not going to fix it.

As far as drilling and catching debris, you can use a decent size shop vac to sit alongside your drilling in an effort to coerce any shavings into the vacuum and not the case.  It's no guarantee that it will get everything, but it's a good start at least.  

Also, it certainly won't catch anything that falls through the back side, but if you advance the bit really slow and only produce itty-bitty pieces of metal shavings versus going fast and hard thus creating big long slivers of aluminum, you better the chances of sucking up the debris. And if something does drop in the case, maybe it'll just be a super small fragment and nothing large enough to get stressed over....and worst case, maybe do a good oil flush and refill after you complete your work.

Lastly, the hardware store sells "picks" that you can maybe use to reach in there and pull the bent piece back out somewhat level.  Or, maybe drill a small hole into the piece that needs pulling back out and insert a screw into that hole and use it to pull against?  Dave/Serow/Versy...you guys know if this is too risky so please chime in  

I think Dave's idea , pulling the cover, pressing the sliver into position, is a winner. Would make checking out debris better.
If the gasket mating surface is damaged, it can be repaired, but, the skill level might be a bit much for someone with limited experience with epoxies and sanding. JB Weld is one fine product. I repaired a sealing surface on a frac pump and it held up long enough to make the job, which means several hours of high pressure, pulsing.
I think you can win that, but, epoxy alone isn't that strong. A stick of epoxy will break, like cement, it needs something to stick to. You might be ahead to find some kinda open weave fiberglass and  press the epoxy into it, putty knife, wet the stuff thoroughly, and dont just wipe it on the case, press it, wet the surface well. The instructions are 50/50,but if you go a hair light on the hardener, and work in a cool place, you'll get a bit more working time.
Once you get it like you want it, hang a drop light by it.
That's incomplete, but a start.

Live I said, just a start..creativity, maybe more than one pass. Sand before adding.