I don't think the Mandelorians would even consider fighting those little buggers, if they would however the Ewoks would be dead. I can't imagine that a Mandelorian would get beaten down by a few sticks and rocks. They were more powerful then that, and all their other ambushes would be avoided or they would survive them...
Still if this would really happen the Mandelorians would probably just leave bored
Alright, let's go with this scenario then:
Ewoks, enraged with the raining of debris over their north Washingtonlike homeworld from the great battle between the Rebels and the Galactic Empire, snag an Imperial shuttle ship, stack it from engines to cockpit with every furry cousin available, and somehow get the sucker flying. They end up on Dxun, crashland at the main camp, landing on a building and killing Mandalore. Also note that somehow, to accomplish this, they would have to have gone back in time 4000 years. These are very industrious Ewoks. Don't underestimate them.