I think he'll still go to Bayern. I could see him renewing and then RBL and BM negotiate a future transfer for 2021. Something similar they did with Liverpool for Naby Keita. RBL keeps him for another season and still get 60m (or whatever fee they'll agree) instead of letting him go for free and Bayern buys him next year when their finances will be better (not that they couldn't buy him now if they really want but I think they'll be financially responsible under these circumstances - more than us anyway).
I hope I'm wrong though and they'll keep Upamecano without agreeing to a future transfer so we can still get him in 2021.
At this point I've totaly given up on getting a good CB and DM/CM (which should be a priority over a forward imo) this year because we'll waste our time and money on Lautaro and Neymar.
Just bring back Todibo. Pique, Lenglet, Todibo and Umtiti (if we get a bid of more than 25m sell him and promote Araujo; don't see it happening though) are far from ideal but I'd prefer those four for another season than spending money on someone not good enough. There are still other talented young CBs whom we could get for cheap but I don't trust Abidal to get the right one. Let's hope I'm wrong and he'll surprise us.
For midfield sell Raki and/or Vidal and return Alena from loan. Possibly Collado can get minutes as well though I'd prefer him going on loan to play regular top division football. Maybe even keep Coutinho though I'd prefer him sold (to free up his wages which we'll need to do if we'll bring another big earner in Lautaro/Neymar) as I don't think he's really a fit here because his best position is already occupied by Messi. Still better keeping him than wasting money on someone like Ndombele or even worse Pjanić though.
We'll be bad next year anyway if we'll prefer to use our (limited) resources on another 100m forward instead of improving defense and midfield but at least this way we wouldn't bring more average players we'll look to get rid off desperately in a year or two. Better save money and go for top targets like Upamecano (if my hopeful scenario will realize) and Haaland next year. Maybe even Camavinga since there are rumours now that Rennes won't sell him at all if they'll qualify for the CL (they are currently 3rd on the table and Ligue 1 is canceled so we'll see how they'll decide). They'll surely lose a lot of money due to coronavirus but Camavinga's value can go even higher if he'll play well in the CL so I could still see Rennes keeping him. I'm 95% he'll go to RM though and we'll regret not signing him for the next decade.