writers note: due to many comments i think i owe my readers an explanation.
Yes Ronon is still the greywaren.
I had the protagonist say that Grey had destroyed the greywaren when he died because, frankly, Ronon is my baby and i would cry if i had to kill him off in a fanfiction.
to put it in a way that the character would see it as. the protagonist said the greywaren was gone because they know that Greenmantle wouldn't keep something alive for very long. the cost to keep Ronon alive, in my opinion would eventually outweigh the reason to keep him alive.
i do hope that this helps you to fully understand why i wrote what i wrote.