The priest whose hermitage the knights have camped at comes rushing over at this point. “Jeez, man, why’d you have to do a thing? He was truly a holy man! If he dies then you’re definitely going to hell, for murdering such a good egg.”
Sir Lionel is not thinking clearly right now. We can tell, because his response to the priest consists of threatening the priest, on the grounds that if Lionel just intimidates the priest enough, the priest will get Lionel out of the whole going-to-hell thing.
But the priest is not having any of it! “Are you threatening my life? I’m an old man; my life isn’t worth much. Especially not compared to Sir Bors here.”
“Have it your own way,” says Sir Lionel, and chops the priest’s head off. “Now to pull Bors out of his armor and slit his throat! That will get me out of this predicament for sure!” Like I said, the man isn’t thinking clearly.
Malory has definitely written himself into a corner at this point. Probably whatever actual Grail romance he’s ripping off has a flow to it. Events stem naturally out of one another, forming a cohesive narrative. But Malory’s in too much of a hurry for that! So instead a Knight of the Round Table that Malory has never mentioned before shows up! Sir Colgrevance! Yeah, that makes sense.
Sir Colgrevance is on the scene, presumably because of the jousting tournament. He sees Lionel struggling with the dying Bors, rushes over, and takes the scene in in an instant.
“Sir Lionel! Have you gone mad? Clearly whatever the dispute between you and Bors was, you were in the wrong!” He grabs Lionel by the lapels and hauls him off of Bors.
“Dang it!” Lionel is in a hole at this point and the only way he can see clear of it is to just keep on murdering. So Lionel decides to make Colgrevance Victim #3. Technically Lionel and Colgrevance joust, but it’s a joust where while Colgrevance is getting his sword out, Lionel starts battering his helmet in.
While Lionel beats Colgrevance to death, Bors miraculously regains consciousness! He’s still in a bad way, but he’s alert and aware of his surroundings. He watches Lionel bashing Colgrevance, and slowly gets back on his feet. Bors is woozy from the blood loss, and he’s still bleeding, but he’s up!
“Bors! Save me, Bors! I’m trying to rescue you!” cries Colgrevance. This would be kind of a dick move on Colgrevance’s part, what with Bors bleeding and all, except that around this point Lionel clocks Colgrevance a good one and he too starts bleeding profusely. So it’s one dying guy begging another dying guy for help, not a hale guy begging a dying guy.
Bors — woozy from the blood loss, remember — starts towards where Lionel and Colgrevance are fighting. But then, he almost trips over the headless corpse of the priest, and he rears back.
That moment of hesitation, of rearing back, is Colgrevance’s death knell. His last words are “Why will ye let me die here for your sake? If it please you that I die for you the death, it will please me the better to save a worthy man. Fair sweet Jesu, that I have misdone have mercy upon my soul, for such sorrow that my heart suffereth for goodness, and for alms deed that I would have done here, be to me alignment of penance unto my soul’s health.” As last words go it isn’t bad, a little wordy. But then Lionel chops his head off.