So I got this idea after I posted the original Stay With Me and I'm so sorry I did
"Cas?" Dean knelt by his fallen friend "Oh god no, not you, not now" he saw the blood soaking Castiel's clothes
"Dean" Cas whispered, blood leaking from the corner of his mouth
"No, don't talk, we're going to get you out of here"
Cas shook his head painfully and gave a small smile "It's too late"
"Don't say that" Dean's voice cracked, a tear running down his face "We didn't come this far just to lose you now"
"Its my time" Cas tried to reassure him "You'll be fine without me"
"You don't know that" Dean protested sullenly
Cas gave a weak laugh that quickly turned into a racking cough, reducing his breathing to a painful rasp. He turned to Dean, a hint of fear finally showing "Stay with me" he asked desperately, reaching for him.
Dean took his hand, blinking away tears, "I'm not going anywhere". He waited with Cas, not saying anything, just sitting, until his fallen friend fell still, a peaceful smile fixed on his face.