Morgan, this has been on my mind, too. I actually just maundered on about it in another context. Here's the gist: I never really was a part of newer, harder-to-die-in games, I think, having come at all of this from AD&D. But I also had three TPKs in two games I ran at GaryCon, and now I'm kicking through some sort of amorphous wondering whether I was too harsh or provided too-few tools or had unreasonable expectations based on the somehow successful never-say-die-ism of my home-game goony players or just am a d*** and don't know how to show people a fun time at a con.
So I set it up this way: I made pregens for every class in the Player's Manual (including the variants like Death Soldier and Fire Thief) so that there would be a range of choices. For Meal of Oshregaal, I just gave 'em all the standard starter pack from Waif of Boreas (which I used for stats, names, races, descriptions, too).
For Ghost Ship, I gave the same batch of pregens 7000 XP and at least one magic item. I tried to make all of these new or unique or gave the character a few scrolls. Most characters were 3rd level, though thief, assassin, and scout were 4th. I assumed above-average HP rolls for the new levels. I also added spells to spell books.
In both scenarios, I let the players assume a "shadow pack" of replacement PCs waiting outside so that dead characters could be replaced after the encounter ended.
For background: Two PCs in the party in my home game (BigPerm's and Brooklyn Book Worm's) have now had 41 sessions dating back to late 2014 and are really close to 6th level. The other players have had many 1st and 2nd level characters die along the way but the ones that have stuck are now 3rd and 4th level and the party is starting to feel its oats. This progression suits my aesthetic sense, and my players seem happy. But I also get the feeling it's a lot slower than many other people's games.
For the con games, maybe I didn't provide enough for less-experienced players to get wring every last drop of survivor juice out of their characters?
There was basically a TPK worth of attrition (some failed saves, a series of which led to one player's Halifax-sized explosion) on the way down through Ghost Ship. And then there was a full-on TPK when they decided to risk a slippery slope without tying off ropes and slid loudly into a pack of radioactive Viking berserker zombies that would have otherwise been quiescent and easy to surprise. I'm not sure, other than providing higher-level or tougher pregens or loading them with magic items, what I could have done to prevent that one other than just nerfing, which doesn't seem quite in the spirit of things. And no one seemed upset or like s/he was having a bad time . . . but it just got me wondering.
I did offer those players the choice of picking up from that spot with a new pack of characters (from the dwindling stack!) or playing an excellent one-page adventure specifically designed for use after a TPK (http://goblinpunch.blogspot.com/2015/04/the-isles-of-dead.html). I kept this in my folder and would have run it in a shot if they had opted for that! They chose to bring down the next batch of PCs, though.
So . . . yeah, I mean, I guess I handled these con games by having extras in reserve. These were both self-contained adventure set-ups, though. I don't know how I'd do it in something more open-ended. I think I tend to prep more self-contained things for cons.
I have no idea how you would have handled a TPK or even a few deaths for Night at the Ptarmigan. I'm so generally impressed with your DMing, though, that I just assumed you had a plan!