Once you get to higher levels, the first combat or two means PCs going absolutely nuclear. I think you need 3 to 5 combats to challenge lv 5 and above. They can handle the heat. If you do less, go way over CR
If I specify "Very Rare Magic Item" it gives a parameter, and even arbitrary parameters can help. It also gets the players thinking I'm concerned in some way with game balance, and though it's true that I'm not, it gives the appearance of that. Someone else was going on about "why don't they...
It's not just destroying the items, its also destroying the formulas that make the items possible. The concept behind the item is wholly destroyed leaving no ability of making anything similar again.
The last part has been stated by previous posters already, but having a campaign arc and planned twists is not "the worst excesses of '80s-90's GM-plotted trad RPGs". One of the top selling D&D adventurers is the Curse of Strahd. Are there planned twists there? Is Balder's Gate: Ascent into...
I’ve got some bad news for you about every adventure ever written that isn’t a straight up dungeon crawl or open world hex crawl. The dmg painstakingly describes writing campaign arcs—I never said that this is a closed world: in fact, I said there’s plenty of other action (determined as time...
I’d consider allowing players return as ghosts, holding the broken pieces of their Very Rare magic items as a testament to what they died over, a visible reminder of unfinished business. Ironically, if they kill the BBEG later, he will rest easy, moving to the afterlife since his goal is complete
The PCs will be destroyed but there is still a campaign world full of vibrant NPCs that can do anything they set their hearts to (provided that it isn’t recovering, re-creating, or otherwise using the players Very Rare magic items)