I'm pretty sure you won't be able to salvage that piston...
I have not seen too many pics of hydrolock damage, but the rods will typically bend pretty bad before a piston would come apart like that. That rod actually looks straight to me, but it's hard to tell for sure in the pic. Something was banging around in there, but hard to say if that's where it started or ended. I guess a hydrolock could have broken up that piston and then the impact damage happened, but that's not what it looks like to me. What do the valves/head surface on that cylinder look like?
+1 on finding another motor to swap in unless you have a friend at a machine shop.