I got mine out by plugging hole and filling with oil, then draining again and the piece came half way through the hole with the oil flow. From there I just pulled it out with my hand. Mine only broke one piece off from what I could tell. I am no pro but I would imagine if that large of a piece was left in the case it would cause some serious damage, but I am sure others on here would know better than myself.

 

the drain plug stripped on my honda 300 (i just looked at it one day, and noticed oil dripping, and tried to tighten the plug) nothing happened. i could turn it all day with my fingers. as it turned out though the plug was wore out (yeah, i know, a plug wearing out? or the threads in the block, and i got a plug out of a honda 500 4 cylinder motorcycle. screwed it in, never had a problem since. (dont change oil that often now though. lol)