In this chapter, Kaido says Luffy is dead. Law confirms it and so does Momonosuke. Momo in particular has a psychic link to luffy, so if he says it, its probably true.
But beyond everyone's words, one thing beyond everything confirms Luffy's death. That is the narration box. If you've noticed, the narration box doesn't declare a victory unless it is absolute.
Like take Kid and Law vs Big Mom. Kid and Law were knocked out, if only for a few seconds, by big mom. Yet in that moment, the narration box didn't declare a victory for big mom. The narration box only declared a victory once the victory was absolute. When Linlin was pushed off onigashima and nuked, she is done for the arc. We haven't heard from her since. Kid and Law's victory is absolute.
My point is, it wouldn't make sense for the narration box to declare for kaido if Luffy was just going to get back up and win. The narration box surely didn't declare for kaido in chapter 1009, nor did it do so when Luffy was KO'd shortly after 1010.
The narration box declaring for kaido means that luffy is done for this arc. He's been KO'd and likely killed. What we saw at the end of 1043 wasn't Luffy, it was Joyboy, just as zunesha said.
When "luffy" finally beats kaido, the narration box won't say Luffy is the winner, it will say Joyboy is the winner.