I’ve done this personal story instance twice tonight (09/19/12) and it’s bugged both times. All my objectives are complete, checked off and greyed out, the Asura engineer is stuck on the beach near where the last tower was located, but no cut scene.
I did notice that in each bugged instance, one or more NPCs didn’t path correctly and got stuck in places in the map. Not sure if the fact that they all aren’t on the beach when the last tower goes down has anything to do with the bug. The first time it was a few Sylvari Wardens, this time it was the pack animal that got caught up the trail on the last leg. These bugged NPCs are stuck in position at the end, the rest of the NPCs follow me around.