Well,if Xebec is really dead,they could recreate him somehow. As we know,if Oda introduces this mhytical figure of a pirate so powerful that he had people like Big Mom,Kaido and WB in his crew,and forced Roger and Garp to ally to fight him,and also attacked the Celestial Dragon,its surely a figure that we will have to know better sooner or later,it cant just be a name dropped and ignored like that. So,if he is really dead,there is two ways to know him better: a God Valley flashback,with also the events that lead to that included,or,reviving him trough a clone!