see if you can use a flat head screwdriver or punch to force it between the bolt head and pan to put pressure on the threads and see if it will come out that way.

if you drill a hole, be careful you don't hit the valve body or filter up inside the pan. maybe go through the side.

but i would just start pulling pan bolts to break the seal and drain it as much as you can that way. it's the safest way.
maybe replace the filter while you're in there. i'd probably replace the shift solenoids too, since they're not very expensive.

then when you get the new main seal in (pay attention to the orientation) then use a little bit of rtv silicone on the tabs. not too much or the cap won't seat properly.

 

Wow! Been there, experienced that! Sounds like some gorilla in the oil change pit used an impact gun to reinstall the drain plug and broke the spot welded nut inside loose. As above, try wedging a screwdriver between the head of the plug and the pan to try to create enogh friction between the pan and the nut to get it out. If all else fails, drill a hole near the plug to drain the oil before you drop the pan. If you try to lower the pan and drain the oil that way, you will create an unholy mess(ask me how I know)!
If you are going to replace the raer main seal while you are in there (always a good idea), there is a trick I picked up from an old Jeep tech during my dealership days. When you insert your upper seal (don't forget to orient it correctly!) leave about 1/8" sticking out below the surface of the mating surface, with the same amount of recess on the other. Do the same on the main cap so that the mating surfaces of the main seal are offset from the mating surfaces of the main cap. Apply a small amount of rtv to the ends of the seals to assure a leakproof seal. I say again, A SMALL AMOUNT of RTV! Too much and it won't seal correctly. Be very careful when mating the cap back on to line up the seal with the gap. A delicate touch is needed so as not to push the seals around and damage them and/or not create a good seal. The old guy had done many raer main seals and had never had one come back. I have done several and only had one leak from getting in a hurry and jamming the cap on and damaging the seal.
Anyway, there are some great threads on this if you search for them!

 

Thanks guys for the great advice. I'm gonna tackle this weekend