I'm guessing Sanji was passed out when Luffy was hit with Kaido's weapon and temporarily died.
OR, Sanji had awoken from his slumbed, only to be greeted with the fading haki of his captain
***
Get up. Get up dammit.
Luffy was still fighting on the rooftop! Probably fighting his hardest battle yet, Sanji needed to pull himself together and make his way to the top as well.
The mossball had also apparently been there, but he had stopped to fight King. Ha! That winged bastard was going to lose, he just knew it.
His long-range haki detected Luffy's spasming conqueror's haki. He was fighting with everything he had, if he focused a bit more; he could feel the anger and pent-up protectiveness from the young man.
Then, like everything slowed down. His haki calmed, surprised?
Next thing Sanji knew.
Luffy's haki was gone. Like an ember lost to the wind.
Sanji saw red.
***
ehehehe... angst? anyone?