In Tasha's Cauldron of Everything, the Swarmkeeper Ranger's "Gathered Swarm" feature states the following (emphasis added):
A swarm of intangible nature spirits has bonded itself to you and can assist you in battle. Until you die, the swarm remains in your space […].
In a recent encounter, my Swarmkeeper just died but was resurrected by the party's Cleric. Because they've died, does this mean that the swarm is lost to them forever?
Best Answer
The book doesn't say, but I would imagine that is not the intent.
As you've noted, the text specifically says "until you die." However, if you rule that the swarm is completely lost upon death, the player now loses out on most of the features of the subclass, making it much worse than other subclasses, which do not lose their benefits on death.
With this in mind, I would assume that the intent is to show that the swarm continues to stay around you while you are dying, but disperses when you are actually dead. Then, if and when you are revived, your swarm reconvenes around you.
Your DM will have final say, since this isn't written clearly in the book, but I would rule that the intent is for the swarm to reconvene and only be missing while you are dead.