Now that we know the Wights come in from the north, I think it's possible to save the World Knot by popping them early. You can't get to them with archers fast enough; but if you run to the allied group and save the dwarves (or at least save their bodies), you'll have enough satchels for a very very long line. Lay a line out from a bit north of the Wight-attacked pylon, move all your forces away from the Knot, and then run your Dwarves in and set off the line from the outer end.
So far, I've popped the Wights early but not early enough to save the Knot. But I didn't stretch my satchel line to the max, and I saved in a spot where the Wights were already attacking. I'm sure it's possible to do better.
MB true Mythmasters have to add to their Homecoming requirements--kill the Wights yourself and save the Knot. :-)
--SiliconDream
