Stronger

Since the first Tyrannic War, the Swarmlord has carved a path of carnage across the galaxy. It was responsible for the scouring of the Megyre System, the destruction of the Brynarr race and the consumption of WAAAGH! Gorgluk. Not only did these events span several centuries, but each was perpetrated by a different hive fleet. It would therefore appear that the Swarmlord's link with the Hive Mind transcends normal physical limitations. If the Swarmlord perishes on the battlefield, the Hive Mind reabsorbs its consciousness through the synaptic web. The Swarmlord is therefore deathless, and can be regrown to face the enemy again, returning stronger each time.

Codex: Tyranids 8th Edition