It's too early for Xavi. And I'm sure he won't accept working under Bartomeu anyway, since he's the biggest supporter and even part of Font's campaign for 2021 elections. By then hopefully players like Rakitic and Vidal (these two hopefully in 2020 already), Pique, Suarez, maybe even Roberto, Alba and Busquets too need to be gone, the only senior or at least 30+ players I still want here after summer of 2021 are Messi and maybe Busquets, but definitely just in a 'Xavi 2015 role' in that case, mentoring our young midfield, mainly FDJ.
Anyone is better than Valverde though, so just for the sake of a fresh start we need to change managers this summer already, my prediction is for Koeman to come in if Valverde leaves, I do think Koeman is basically the only realistic candidate I could see Bartomeu appointing, because he's still a safe choice, and kind of a yes man, but at least he's got better personality and judging by Netherlands we see he can make his teams play really attractive football. And then we give him one season and if we like what we see, maybe he can stay for an additional year or two under the new Board, with Xavi initially returning just as the assistant manager or even Barca B manager, like Pep started. Otherwise, appoint Xavi right away and Koeman goes back to his Netherlands gig, I wouldn't even mind Koeman not leaving that post to take over Barca, if it's only for that 2020/21 season, he can do both for one season, I guess, but if he stays longer, then he must leave there and focus only on Barca.