Silverweed lived in the warren of the shining wires, maybe since he can remember. He was forced to tell stories to the other dwellers. I think, because of that he never will trap into one of the shining wires. Cowslip will take care for that, because he needs Silverweed. His stories are the opium of his people. Because of that, an enormous stress lies on Silverweed. So it's impossible for him to be happy.
Then, Woundwort came and Silverwwed became a slave of the dark one. He left the shining wires behind but his new life was even worse. He has not only to serve Woundwort, he must see the destruction of Redstone without knowing, if anyone survived.
Then, he was freed by Watership Down and for the first time in his life, he experiences, what freedom and living without fear is. For the first time in his life, he has friends.
And only weeks (or maybe month) later, he sacrifices his life save the people who are meaning everything for him.
So he only could find real salvation in death.
I think, he has one of the saddest fates in Watership Down.