Helicoil and stau with stock size bolt?

Drill out an tap for next size up bolt?

At least I didn't snap the bolt like someone I know did once...at the racetrack...trying to fix my crappy bike for an endurance race...at the WERA GNF.  

Is the head off the engine?  Not that it matters to which repair technique you decide on - you'll generate chips either way.  Just be careful about letting any chips fall into the engine, but no need to tell you that.
I think if it were me, I'd heli-coil & use the original bolt.  Using a larger bolt means you'd have to drill out the hole in the cap, too, & then there's no turning back.  Also, a larger bolt is a stronger bolt & might well apply more clamp load (what would you use for a torque?) which could distort the cap & bind the cam.
Just my humble opinion.
Sorry about your bad luck.  Hope it all works out.

Without a doubt, Helicoil.  It's a quality repair you can take pride in.  And, no drilling the cam cap.

Ok, done this a few times too, here is a trick for you whether you go larger or not, take your tap, and give it a good smear of Lithium grease, as your cutting the threads, the grease will catch and hold the cuttings. as a precaution, try to stuff some rags around the area to help catch any cuttings that get away.