There are quite many options at Bayern Munich actually when we check their squad. Let's say Sommer didn't leave then there are 4 goalkepeers available as alternatives to Neuer. One of them is a really young one and let's say we kept him outside. Ulreich, Nübel and Sommer are the ones left.
If Neuer doesn't start playing right away then Bayern Munich can actually reassure Sommer about being the main goalkeeper here. In that case Sommer wouldn't leave and the problem would be solved. Otherwise Nübel can be a decent choice maybe until Neuer gets ready to play.
Yes it's true there are lots of options for Thomas Tuchel in the goalkeeping position. If it's true that Inter Milan are interested in Sommer then Tuchel won't bother thinking about it. Because it is likely that Manuel Nuer will be able to rejoin the Munchen squad when the competition has started, considering that the Bundesliga will start the match on August 19 and Nuer still has one more month to completely recover from his injury.
If Nuer cannot recover faster, Tuchel still has two replacements namely Ulreich and Nubel, It is likely that Ulreich will be more able to be relied on by Tuchel next season. I think Munchen weakness in failing to win the Champions League last season lies not in their goalkeeper but in the striker. Currently Munchen is desperate to bring in a suitable striker like Hary Kane, if they manage to hook him then next season Munchen deserves to be included in the list of favorites with Madrid and Man City in the Champions League.