If he actually ends up accepting and coming in the next week, I could very much see Puig getting promoted right away (especially since Alena is now gone on loan), and us selling at least Vidal to Inter before the January window closes, since they already declared Vidal is basically their main transfer target (they're even putting the Eriksen talks on hold because of it, even though he is much easier to get) and Vidal is the literal opposite of what a Barca midfielder should play like, so he's much more likely to leave before Rakitic, who I'm guessing would stay for depth until Alena comes back in the summer, and also there's not much interest in him in January anyway. Maybe Roberto would be permanently moved to midfield too, as I could certainly see Xavi giving Wague a fair chance, with Semedo probably taking the starting spot. Don't think Xavi ever saw Roberto as a RB.
And like you said, It's not just about the pure positive way of setting his team up to play the Barca way, he'd also be a much needed breath of fresh air in terms of the psychological effect. The club needs this, the psychologically ravaged team needs this, and we the fans certainly need this. Even though I think it might be too early and I still don't think Xavi will accept working under this Board, as it could very much damage his relationship with Font before the elections, I'm still hoping the call for help, which the club of his life desperately needs ASAP, will be enough for him to return early.
And I think Xavi knows nothing is guaranteed, so turning down the Barca job now could come and bite him in the ass in the future (maybe Font doesn't win the elections, and then he maybe wouldn't come back in 2021). Plus as much as I hate Bartomeu, it's like someone else already mentioned, he knows if this works out, he could turn from the worst president post Cruyff to a hero (at least to some Cules, I for one will never forgive him for making us a laughing stock of Europe for the past 2 years, even if Xavi comes in tomorrow and wins this season and next's season's CL), who fired our worst manager ever and replaced him with Guardiola 2.0., all in less than 2 years. This is Bartomeu's last push to try and get his candidate for elections a fighting chance in 2021, cause right now, I can't imagine anyone in their right mind would choose his candidate. Anyway, I guess we'll get our answer soon enough (if Xavi really is ready to reveal his decision after tomorrow's game). And if the offer to him from our Board is actually true, of course!