First of all, if the escort isn't following the bomb, don't panic. Take bomb to incinerator and run back to where escort is standing. You'll still get your ash.

For Coerthas, at least for Eastern Highlands, 58,30 is correct coords. For me, soloing it, was not so easy. I did not die but you have to keep the Bombard King from dying. You can buff the Bombard King and heal it but that's the least of your worries, as you'll have to deal with Dreadwolves (25-29) and Footpads (there was 1 inside the tunnel leading to Owl's Nest) The spawned Elementals were easy to dispatch but they do hit Bombard King fairly hard. You need to complete the escort in a set amount of time (I'm guessing about 15 min?) before it explodes. This is better to do as a group or as an R40+ where you can just kill w/e you come across (or at least be able to avoid aggro on Dreadwolves) Ranged classes will fair a lot better than melee because you could stand a bit away and not aggro local mobs while you pick off the Elementals.