In my most recently played campaign, I was playing a character that was eventually supposed to betray the party. I got killed long before that for being a general problem character.

So my character had gotten a horn early on that, when I blew it, summoned a literal army of subservient goblins under my command, which we used to build/defend our base of operations. Unrelated to the TPK, but a funny thing came out of it because of the TPK.

Kujo (the character) was probably close to true neutral, not doing good or bad unless it personally benefited him. At some point he gained a potion that, if he didn't drink some of often enough, would turn him into a spikey godzilla-man of some sort. Kujo loved this cause it made him stronger in every regard.

At some point, while wandering around a town, Kujo came across a couple of kids from the local orphanage, and chose to "adopt" them (he basically said 'you're coming with me' and never spoke to anyone at the orphanage). After Kujo gave them some 'soda' (which were just extras of the potion from earlier) one kid sprouted wings from their back and the other turned to living stone like the Thing from Fantastic 4.

A few adventures later, one of our party members is getting testy over Kujo's chaos, and brews a couple of the potions with poison in them. As they watched Kujo down one of the poison bottles with no effect (level up had coincidentally JUST given him poison immunity before that session), and watched him try to hand the extra potion to the kids (who needed it as well).

At this point, the person trying to poison Kujo jumped into action, not allowing Kujo to poison a child with the potion that they had made to kill Kujo. Immediately casts Disintegrate, which I passed the save for somehow, and Kujo beats it as fast as he can, chased by the other player.

I don't remember how, but I failed some kinda save during the chase and fell prone, allowing the other player to catch up. Between the Near-disintegrate and other spells thrown from the player at this point, Kujo was lucky to be alive. Which the player corrected almost immediately by curb stomping what remained.

Now, remember those goblins? The entire army that was effectively running our base and doing all the logistic stuff while we were out adventuring? The one that was summoned when a horn was blown? Summoned by Kujo?

Yeah they all just popped back out of existence with his death. Everything that was being done at base suddenly stopped. Our support network was effectively gone. We went back and the few non-goblin allies we had were cleaning up the mess, putting out fires where goblins disappeared while holding torches that fell after the goblins proofed, picking up tools/supplies that had been dropped, everything.

Honestly that whole campaign was just fun, and the TPK was the cherry on top that made it so much better.