misfiring wont kill a piston, and with a fire on and off thats what you get, maybe if it was sparking on upstroke or something it could damage internals but you wont want to be driving anywhere with it trying to fire back, i expect it would smash its mounts if it was even possible

while the engines are disposable they are also very easy to change
once the front end is off you can whip it out easy
i bought one that threw a rod because of low oil, took the front end off almost whole, threw in a 3000 mile engine and off it went