Dead men naked they shall be one With the man in the wind and the west moon; (2-3)
We understand from the very beginning that death in this poem is a new beginning rather than the end. Those "dead men" will have a new kind of cosmic afterlife with the wind and the moon. Which actually sounds kind of fun, if we may say so.
Though lovers be lost love shall not; And death shall have no dominion. (8-9)
The physical bodies of those "lovers" may be gone, but their love carries on in this cosmic afterlife. So death has no "dominion" over the most important things in life, like love. Nice try, death, but we've got you licked.
Though they be mad and dead as nails, Heads of the characters hammer through daisies; (24-25)
Our mortal lives might be "mad" but there's something about our "characters" that endures even after death. So no matter how crazy and dead our physical bodies may end up, the better parts of ourselves push through those daisies growing over our graves.