It’s not going to hurt anything inside there, the screen on the oil pickup will keep it from being sucked into the oil system. If you hit a big bump in the road, it might rise up high enough to be hit by a crankshaft journal but I don’t think that will hurt anything.
If the current thread size of the drain plug is 12 mm, then you could tap the bung to 14mm. If it is already 14mm, you could tap to 16mm and use a drain plug from a Subaru. Get the Subaru plug first because I think it is a fine thread.
If you take the pan off, why not just replace it? Assuming this is the 2nd generation Kia Rio, an aftermarket oil pan with the correct drain plug included sells for about $78 on RockAuto. Add shipping, tax, and the cost of a gasket, and you are probably at around $100. A Heli-Coil set, or similar product costs about $80. Replacing the oil pan appears to be the better buy.
It’s a toggle bolt. You you might want to try to flip the toggle using a dentist pick, but that is a long shot. They are designed not to come out the way they were placed into that hole. I wouldn’t worry about the magnet. It won’t go anywhere.
If one pulls it out backwords it should be fine as it is the same size opening as when it went in. Maybe hook through the hole with a piece of bent coat hanger like a j
Don’t the parts stores sell individual heli-coils anymore? They did when I had my 71 bus. I knew guys that raced VW engined midgets and they put them in all their heads because the steel threads made it so much easier to change plugs.
I think it’s safe to leave in place. It can’t jump up to the screen or the crankshaft. Even if it did, what then? I would get a new plug, a jug of oil, and finish the job. Something some day may finish this engine off, but this will not.