But I feel like Law's death actually makes sense
- his dream is the same as Robin's and in order to accomplish it, he'd effectively have to become an honorary straw hat
- So far, Luffy doesn't give a single shit about the will of D. Law is the only D he is close too. If Law dies and imparts his will onto Luffy, now Luffy will have to care about the will of D as well.
- Kid and Law are facing off against an all out big mom, whereas they had to go all out just to injure base big mom. They are basically fucked and one of the few things that might be able to turn the tide of the battle would be immortality surgery
- immortality surgery is a chekov's gun. Oda wouldn't introduce it if Law wasn't going to use it at some time. Him using it on Luffy or zoro would kill the tension of the story, which is why Oda wouldn't do that. Him getting mortally wounded and giving it to Kid seems like the next best option.
Ultimately, in this chapter, Law posed a question to Kid about the upper limits of his magnetism. If these limits are extremely high, only limited by Kid's stamina, then immortality surgery might honestly allow Kid to defeat an all out big mom. Basically, the way I look at it, immortality surgery boosts one's life energy to insane levels. If lifespan=soul, immortality surgery would give Kid a stronger soul than even big mom's.
This would boost the stakes of the fight. If Kid loses and gets his soul stolen, big mom would get access to a soul even stronger than her own, making her far stronger than before.
By giving Kid near unlimited life energy, he would no longer have stamina issues and would be able to use magnet awakening unrestricted, which would give him fujitora level feats.