It only recently came to my mind, how important deaths actually are for the story of One Piece. Over the course of the story, almost every main character has motives/actions inspired by the deaths of loved ones and friends.
1-Zoro: His past has been the object many discussions especially in terms of “Is Kuina still alive?”. Personally, i do not think that it really matters this much anymore. Zoro believes her to be dead, which is what drove him to carry out her and his dream of becoming the greatest swordsman alive since this was a promise they gave to each other. There are literally dozens/hundreds of people in the OP universe trying to do the same thing, become the best. Would Zoro have been able to put as much effort into his dream as he has, if he didn’t think Kuina was dead and wanted to fulfil their dream on “her behalf” as well?
2-Chopper: His past is well documented in the Drum island arc. He ate the Human Human Zoan type fruit and became able to talk to humans all while gaining the behaviour of a human. He befriended Dr. Hiluluk who tried to teach him everything about the world of medicine and his desire to cure all diseases in the world. Not only did his best friend and father figure die, but it was also (arguably) Chopper’s fault to a certain degree on top of that. I do not believe that without the death of his best friend, and nothing to hold him on Drum Island (with he exception of Doctorine) he would’ve been able to leave the island and roam the seas with the Straw Hats in order to fulfil his friends dream, even though Hiluluk himself seemed to compare himself to pirates (skull flag).
3-Brook: The entirety of his crew gets wiped out with only him left alive. He would’ve tried to reunite with Laboon regardless, I guess, but would he have been as passionate if he wasn’t the only one left to fulfil the promise he and his friends made?
4-Nico Robin: Like, do we even have to talk about her? Her entire island was wiped out by the Government because of their archaeological knowledge of the Void Century etc etc. of course, this has been the most driving factor for her to uncover the history of the One Piece world.
5-Nami: Her stepmother died, trying to protect her and her sister. Even though Bell-mère was a marine and you could argue that her impact on Nami wasn’t this strong (with her becoming a pirate and stuff, you know), what her death surely left her with was a good amount of hatred towards the Fishman race. This was one of the main triggers of her story arc, but also drove her motivations and character development of later events, such as meeting Hachi and Keimi on Sabaody. It also perfectly transitioned the world in the race dilemma the OP universe is in, with Nami being a prime example of how it could be resolved: forgiving the past actions of the different race based on the purity of their actions in the present.
6-Sanji: Born the “odd one” amidst his 4 siblings, he discovered his passion for cooking at a very young age. For this he was ridiculed by his brothers and cast aside by his father. The only one encouraging him to live the life he wants for himself were his mother and sister. With his sister being of the same age, I believe his major influence was his mother especially since his father did not give a damn about him. With her death, nothing really held him in the Germa Kingdom anymore. She also encouraged his cooking.
7-Luffy: He wanted to go out to the sea as long as we know him, being mainly inspired by Shanks and his crew. Regardless, Sabo’s death (he did not know that Sabo survived until Dressrosa) must have had some impact on him in terms of the seriuousness of his cause, now shouldering the dream his friend that passed. Same goes for Ace’s death: not the reason for his departure for becoming the Pirate King, but surely more motivation.
8-Franky: He lost his mentor Tom who was confirmed executed in Impel Down for his crimes of making Roger’s ship/being framed for an attack by Cipher Pol No. 5. This caused Franky’s resolve to create the best ship in the world.
9-Usopp: He lost his mother and Yasopp left to be a pirate essentially leaving him alone all his life on a dull island where nothing happens until Luffy and co show up and expose the troubles. This caused his resolve for adventure.
All I want to say is: out of almost every death in One Piece, the crew or a crewmember gained motivation, thus advancing the story of the Straw Hat Pirates. Because of this, I believe we’re in for another death (this time maybe even of a character more prominent to the main story).