Part of Khan had expected the doctor to faint on him.
Another part, however, becomes incredibly nervous at the sudden change of events; To make sure that the other is still alive and has not just died on him, Khan briefly lets go of John's arm to feel for a pulse at the neck instead---
It's there. It's rather strong even, and continues to grow stronger the more seconds pass between them.
Which means that Khan's blood is working, that it is healing Watson, fighting against the poison while repairing the damage that has been done.
Good.
Yes, good.
---Thank fucking god.
The relief that washes through him is of such intense nature that it causes Khan to shiver for the briefest second - his composure is collecting itself soon however, attention focused on the task at hand once more. Slender fingers returns to the other's arm, holding it steady as Khan keeps their injuries pressed together for a little longer - they're not done yet, after all, John needs more. A lot more.
They're back on board of the Enterprise.
After managing to hold their position for a bit longer, Khan - as well as the other security officers - had been able to request backup, which had promptly appeared in the form of more security, more shuttles, more efficient weaponry; They're not meant to fight in wars, definitely not, but they're equipped to defend themselves - that's something, at least.
So, in the end, they'd been able to carry the injured ones away from the battlefield, bringing them back up to the ship - including Doctor John Watson, who remained unconscious for the whole of the act. He'd been brought to Medbay, where Doctor McCoy had taken over - but since Khan's blood has managed to keep the other alive for so long, even helped him recover to a certain extend, they had agreed to have a proper blood transfusion going to get more of that liquid into the seriously injured man.
So, Khan has done precisely that; Given more of his cells to John, which had improved his vital signs immensely over the span of about half an hour. It worked so well in fact that - once Watson was stable, the poison removed completely from his body, inner injuries healing successfully so - Khan had then proceeded to give more of his blood to other crewmembers who had also been hit by those daggers, effectively saving most in this way.
Hours have passed since then, the ship becoming quiet once more, things calming down a bit in Medbay as well. Khan himself sits on a biobed across of John's own, being monitored by some medical devices as he's given quite a lot of his own blood; McCoy had insisted for him to stay, just in case the immense bloodloss was going to kick him into unconsciousness as well.
It did not, but Khan can still feel it, the exhaustion that clings to his bones. He knows it's only a matter of time - a couple of hours, perhaps - until he'll be completely fine again, and he also knows he could, in theory, just go on with his life. No need to keep him here.
But he won't complain.
So he just sits there and waits, gaze occasionally trailing over to the blond he's managed to safe from sure death.