Locked at 5/6 runeseeker Quest

When I got to plunderers point I set all the bombs and could not hit the detonater no matter what direction I tried from. So I went out and restarted the instance, when I went back everything had disappeared and now it won’t unlock the last part for me for the 7 rune slots on shrines. Is there anything I can do in lvl 82 and would really love to have to start over