I have yet to witness successful castle capture in situation when teams have decent gear and are about even. Closest to it was NA siege where we (attackers) lost because of bugged flag on top of broken wall...
Tonight's siege, where I played for Kalmar vs Ni was pretty much half of our team jerking around while us others were in try hard mode for two hours. Think I've put down around 50 flags, but no use. Of course, that siege showed us how truly broken range is atm. Spawn isn't exactly killometers away from castle walls but isn't near either, yet archers had it pinned down.
My bet is, Wolves got no chance to get that castle. Especially because Mercs will probably have awesome roster, full of ranged scum.