Hey there!
For some time I thought I was the only one with that idea
I actually did not run
Red Hand of Doom mainly bacause I started
Tyranny of Dragons when the adventure came out, and now (almost 3 years later) the group is at level 12.
But I took things a little bit too far, I guess.
(Arc I - Done) I introduced 4 more factions to the game. The mercenaries from the shadowfell from the beggining of
Scales of War, the Chuch of Tiamat because it's a totally different thing from the cult and there is no reason why they are not helping, the Githyankis from
Scales of War, again because there is no reason why they are not helping, and a 4th faction that has to do with the background from one of the players (basically good guys turned bad guys). I ran
Hoard of the Dragon Queen up until Waterdeep, then the group got separate and I ran
The Shadow Rift of Umbraforge for one part of the group before turning the full group to the flying castle in Hoard of the Dragon Queen with a twist, they were intercepting a reunion in the castle between the cult, the church and the shadowfell mercenaries. Things went south pretty fast but somehow they got the castle.
I then ran
The Temple Between adapted to the campaign in Baldur's Gate, but duo to that fourth faction revealing themselves traitors, the city fell.
At this time the campaign was totally different from
Rise of Tiamat, so I scraped most of the book, only reading it as a guide for some things and for the Council of Waterdeep (Heavily adapted). From Rise of Tiamat I'll run the Xonthal Tower and the trip to Thay, I guess.
(Prologue to Arc II) Oh, and Neverwinter also fell along the way (Things are pretty rash). The summoning will be there using part of the city as sacrifice.
I really liked the idea from one of you guys of using a consort of Tiamat instead of her in the summoning and have the summoning fail.
(Arc II - Going) Before the siege to neverwinter, I plan to run xonthal tower, a tournament to get allies from the Ruby Dragon and the final two adventures from the Paragon Tier of
Scales of War to avoid reinforcements. I may throw the Ruby Dragon idea out and leave it for after the summoning or throw it all out.
(Arc III - To go) Then there is the recover of Baldur's Gate and the
Palace of the Red Parsha -> City of Brass thing but I'm still figuring it out how to put it all together because I can't seem to find where I'll put the death of Bahumut there, and there is one more thing from the campaing... the plot twist
(Plot Twist Prepared) The leader of the faction that betrayed the players at Baldur's Gate is actually a simulacrum of one of the leaders from the Church of Tiamat, which is Shruppak, that is actually trying to fool everyone alongside The Sibilant Shade (one of the leaders of the cult, highly devout to Null) to summon Tiamat only to have a clear opportunity (during the summoning) to kill her and use her essence for something (Haven't figured it out yet, maybe become a god (Shuruppak) or goddess (Sibilant Shade)), and if that happens how in the nine hells am I to put it all together with a big battle against Tiamat at the end of the campaign...
I'm in serious doubt at what to do with the plot twist... If I leave for the summoning, it would be at least weird to have Tiamat killed, ressurrected (when they put out the Sibilant Shade) just to have them go to hell to kill her. If I leave it to the end, like they think they're doing good in killing Tiamat only to leave the space to another god (all planned from the start, lolz), I think a battle after Tiamat would diminish the epicness of fighting her, even if it's against an Epic Warrior and Shadow Dragon with divine powers...
Any suggestion on that Third Act and the Plot Twist? Throw it all out and make it simple? Go along?