This is baseless speculation. If oda wanted to show Momo's willingness to sacrifice himself he'd have had momo actually try to sacrifice his life to save someone in a big dramatic scene, not simply make a selfless request and get denied.
It's not BASELESS, it's literally in the fucking chapter, he wants to make the sacrifice and is denied by Shinobu. That is a big dramatic character moment...
Momo started this arc frustrated by his age and that he couldn't fight Kaido, and had to rely on Luffy, now he is doubting Luffy and himself and thinks he needs this to pull through. Don't doubt Luffy, it's One Piece... If Momo gets permanently aged that reaffirms the idea he is right to doubt Luffy, Luffy asked him to fly him up to the fight, not take on the fight himself...
Momo has had 2 or 3 major scenes already this raid where he has made what would likely have been "life ending" choices: telling people to focus on the raid when he was kidnapped, stabbing Kanjuro, declaring his name.