If the hex hole is damaged you will have to use a dremel handheld hobby grinder/cutter disc, and carefully cut the head of the screw to have 2 parallel flat sides, then use a tight fitting spanner (or mole grips) to tightly grip the head and hopefully unscrew the screw.
These screws are very tight, and they are fitted with locktite. If they were loose and allowed to ‘rock’ in their holes the holes would soon be worn and the joints weakened.
Failing that - the heads could be cut or drilled off and then, with the pin off the bike the remaining threads could be drilled out and the holes re-tapped or threaded. This may need an engineering shop tho’ … I wouldn’t like to have to do it … like root canal work on teeth , good luck !!