The heroes started out the climactic battle already fairly chewed up from their fight with Azarr Kul; sirfox's gnoll cleric of Lathander remedied this by successfully using an up-level scroll of mass heal he'd picked up for just this kind of scenario. (~4,000 gp well spent!) All of the NPC allies were taken out in the first round by a blast of cold from Tiamat (12d8 and not one of them made their saves — ouch), leaving the PCs on their own against a CR 13 beastie with a bad attitude and some hellacious attacks should she be able to get them in. laurie_robey's sorceress fell to another breath weapon attack shortly thereafter, but not before getting a few solid fireballs in. hantamouse's archer Dreklin, who started out the campaign terrified of even hearing the word "dragon," was downright bloodthirsty in his attacks with his dragonbane bow ("No surrender!" pyew-pyew-pyew), and was pulling off some industrial-strength dodging to avoid her breath weapon attacks. And of course, jamesbarrett's wild-eyed bard-barian Balgor, always working on that "Dragonslayer" title, leapt atop the dragon goddess's back and brought down the killing blow just as Tiamat was rearing up over Dreklin and about to use her full attack on him and him alone.
Balgor then took 25 hit points of crushing damage from having a dead Aspect of Tiamat fall over on him. But he figured it was worth it.
From there we had a very pleasant little denouement in which the characters briefly revisited (or at least had mentioned) the various major NPCs or friendly locations, were given heroes' welcomes and treated like stars, and all named Knights of Elsir Vale. There was then a final shot of them all gathered wearing medals, the music rose to a crescendo, and the credits ran. Figuratively speaking. ;)
All in all, Red Hand of Doom was a great adventure, and worthy of its place alongside such classics as Against the Giants or Temple of Elemental Evil. And while I added a few flourishes or made a couple of tweaks here and there, for the most part I ran it straight as written (which is something I almost never do) just because it really didn't need a lot of adjustment.
So, I'm very pleased! It's only the second campaign I've run that "finished" rather than just sort of coming to a stop (the other being Star Hero back in the '90s), and it was a fun one. :)
Next for me, a short break from GMing, then time to finish up that Star Wars scenario from last April. 0.o