If he wanted to spend the appropriate time to learn a new style of guitar, yes.Should he have even tried?
You don't accept a gig like this if you have an injury. There is no excuse for this kind of performance. None. Zero. If you can't do it, cancel the show or find a replacement.Uh, did everyone forget that his arm became so fucked up that he disbanded Megadeth for a good while? He put the band back together but that doesn't mean his hands are 100% healed, just in good enough shape to tour.