While fighting the wither with another player, we died and went back to spawn because he broke our beds. When we tried to return to where we fought the wither he was gone. We looked all over the area, even going back with our elytra's to double check that he wasn't there. He was at half health when he destroyed our beds and when we went back to spawn. He was doing his dash attack and was on the surface right before we died. And after, we looked at the damage to the terrain and it just stopped right were we had died.