Most and least replaceable SH?

[Warmmedown]

Which SHs would be hardest and easiest to replace, with respect to their practical function in the crew? Let's assume they leave the crew either at the timeskip or right now (Kaido arc or later).

I think hardest for now would be Franky. Other shipwrights could fix the ship, but the escape functions he added to the Sunny I doubt anyone else would have come up with.

Later on Robin's probably going to irreplaceable, when it comes to getting to Raftel.

I think most replaceable is probably Chopper. He's not that strong (unlike Sanji or Zoro) and there are plenty of good doctors. Leave Chopper behind and let him feel the pain of rejection for the 3rd time. A man is dead when he's forgotten but Chopper isnt a real man so it's not murder. I could say Brook, but Brook's soul-body separation is pretty useful.

 

[SSJ2]

Most: Luffy. The guy literally adds no value to the crew aside from being strong.

Least: Franky for reasons you've stated.

 

[Captain Cadaver]

Most replaceable would be either Chopper or Luffy. Law can easily fill Chopper's place and beyond strength and charisma, Luffy ironically has little of value for a captain beyond his plot armour. If anything, his leadership has been a detriment more than a help. Brook is also a candidate if talking purely about their crew roles as a musician is the least essential job here, though his actual skills have consistently come in clutch for the Straw Hats in the New World.

Least replaceable would be Franky or Nami since you can't have a crew and ship if the ship gets damaged or you have no idea where you're going and do so as well as these two do. Robin is another honourable mention when speaking purely of the crew reaching their endgame (Raftel), though less so when talking purely about journeying the seas as a glorified crew.