i finally managed to figure out what was goin wrong...
i gave it a new try to bake the animation with maya's own option, so i took one rigid body grp after the other (important here is to select every single debris), then pick option in bake options "out of channelbox" or similar, select attributes which change and bake the animation.
After that u just have to disconnect all the rigid bodies from the objects, in my case with ruins' own option "disconnect rigid bodies".
and that's it
made me kinda rage but hey