Nasty situation.
An over tightened bolt shoulder against the cover face with likely oxidation of steel and aluminum threads under tension.
I have had a couple cases where with a tight fitting 6 point socket wrench on a solid bar and a sharp deliberate rap with a 16oz plumbing hammer, the bolt came loose with a bit of a snap, along with heating the bolt as best as can with a MAP gas torch. Scary, i know. (Once had an over tightened drain screw on oil tank as well.)
I don't think you'll twist out the threads in the crank case, but if you cannot find a tight fitting wrench, you may have to resort to potentially brutal but careful and deliberate measures.
I had one like that a few years back. The hex head was already trashed prior to my aquisiton, use of wrench out of question.
Could not grip rounded off head with a Vise-Grip.
Drilled a hole in bolt and attempted using a large Easy Out. Tried heating the bolt, the heat was rapidly absorbed by the alum.oil filter cover and crank case. Because the bolt is hollow, the Easy Out just expanded and broke the bolt, the Easy Out could not hold.
Had to resort to hack sawing around circumference of cover, then taking a hammer and a large piece of steel, breaking apart the part of the cover closest to the crank cases. Then was able to slide the top remaining piece of cover towards crankcase. With the tension off the threads, using a small pipe wrench, was able to unscrew bolt without nay problem.
The good part is the finned filter covers are not scarce, the 14 mm bolt is another situation.