First off, I recommend this guide on the Giants in the Playground forum:
http://www.giantitp.com/forums/showthread.php?t=171284
Second, I played in a Red Hand game. There was a fair bit of turnover. Our group consisted of:
The Core Four
Jehosophat, fire genasi wizard
Achaea, human knight
Hibiscus, elf duskblade
Grim, human ranger (mounted archer)
Of that group, Grim died twice and came back via DM bargaining shenanigans. I mean, his name was Grim, so the idea of him digging himself out of a shallow grave after the party thought he was dead seemed to fit. The second time he died his horse carried him away from the battle, and eventually we decided that he was a revenant, who'd only stick around long enough to thwart Tiamat.
We also had a couple PCs who replaced Grim for a little bit of time, plus two players who kept churning through PCs.
The Roster of Dead
Figo the gnome dragon shaman (killed by green dragon)
Random half-elf shifter druid (killed by greenspawn razorfiends)
Random human barbarian (killed by a harm spell when we decided to attack the lich)
Steve the dragonborn dragon shaman (killed by hobgoblin archers)
Random halfling cleric (killed by hobgoblin assassin)
Queequeg the half-orc harpoonist (killed by blue dragon)
Random dwarf sorcerer (killed by falling)
Random human ninja (killed the Aspect of Tiamat)
If you want to keep character turnover low, you might want to adopt a "TPKs Only" policy, where PCs can only die if the whole party dies, if the rest of the group abandons them, if they suffer massive damage (50+) that drops them below -10, or if they're coup de graced.
Also, the best advice I saw for tweaking the adventure is to make the Big Red the final dragon they face. Shuffle things around a bit, so that an actual blue dragon guards the lich's sphinx-base, and so a white dragon guards the fortress in the mountains. Then have the order go something more like this:
* Encounter Red Hand, not realizing they're an army yet.
* Sneak into the mountain fortress, kill the white dragon, realize that a whole army marched out of here.
* Head to take out the green dragon at the bridge, destroy bridge to slow army down.
* Go slay the black dragon in the swamp.
* Learn that a lich is aiding the army, so head to the desert and fight a blue dragon to reach him.
* (Decide that liches can go to hell and nearly get the whole party killed by charging an enemy far more powerful than you.
Optional. It worked for our party, thanks to a lucky dispel magic on his anti-life shell, followed up by a thwack from a staff of healing.)
* Rush back to Brindol to defend the city and defeat Azarr Khul, mounted atop a red dragon.
* When the big red dies, Tiamat's ritual is complete -- she simply needed sufficient carnage and the deaths of five dragons in a close area, which summons her Avatar to the mortal plane.
Good luck, have fun, and may your players always show up for game night.