hm, when you set bpathcolliding in the default properties of the blocking volume to true, and then rebuild the AIpaths, then you will get the message that pathnodes cannot be based on blocking volumes. so it does not work with blocking volumes at all. you will have to find an alternative way for your idea. i would use movers but i'm pretty sure it won't work with them either because of the same problem. navigationpoints cannot be placed on movers :/.
i would make a invisible bridge which has the pathnodes you need and an invisible barrier in front of the cliff so you and your squad can't enter the cliff. then, after the atte falls down, make the barrier disappear. you should set bpathcolliding of the barrier to false, so the path can get calculated when you "build all".
oh, and its not that important but your squadmembers could try to go across the bridge before the barrier disappears. they will ignore the barrier because its not colliding their path. could look quite stupid because they will run against an invisible wall. use blockedpathnodes instead of normal pathnodes. when you trigger the tag[which you have to define in the defaultproperties of the pathnodes(event>tag)] of the pathnodes they will get activated and the squadmembers will use them.
not the best idea, but i hope it helped.