It would be boring. I rather give up this campaign.A proactive aproch of defeating single lords and gathering(small) armies is much better then joining in for some blowout battle.
I will rescue say groups of 3 or less, but more then that and you are very likely to get somebody killed.
Lets just assume they're all going down, as AI is dum and probably will, if you go in with 5 allies it's a 50% chance one of them will die for good. Yes you can re-load your save, but who wants to do the battle again?