The swordsman knew at this rate that he was going to die by drowning. Of course, the water drowning him is special, but dying this way and not at his enemy's hands was clearly an insult to him.
He had two choices to pick from. The first option is that he could refuse to regenerate his flesh so as not to waste his lifespan dying this way. But this option would cause his Cave Heaven to become exposed when his body is destroyed.
A divine being with a Life Fire and some lifespan who refuses to regenerate their body will not escape death. They will only force the battlefield to shift to their Cave Heaven.
In a situation where an enemy can kill you outside of your Cave Heaven, it is unlikely that you will be able to gain any advantage within your Cave Heaven. In fact, it is more likely that your Cave Heaven will be destroyed by exposing it.
The second option is to accept his loss, keep expending his lifespan to protect his Cave Heaven, and die without a chance to turn the tide.
