Maybe I'm being naive but I feel the chances of the Brewers leaving Milwaukee border on zero. It would be cutting off their nose to spite their face, which MLB is definitely known to do from time to time but there are mitigating factors this time around, I think.
First, there are no truly appealing markets to slide into. When you're talking about places like Nashville, your long-term prospects at a new location aren't great. The Carolinas have some appeal but I just haven't seen a ton of effort locally to bring in a team (if that was the case, the A's should be moving there).
The Brewers had fringe top ten attendance from 2017-2019. They were mid-pack last year and will likely end up there again this year, despite a disappointing 2022 (ticket sales trail performance by one season). Where else is the franchise going to get that kind of long-term support? Sure, they can probably get a shiny new stadium and 3-4 years of packing the place but what happens after that?
Milwaukee has a long tradition of supporting baseball in solid numbers. It's not going to be easy to replicate that anywhere else given the size of the markets we're talking about here.
I think it's interesting that people have largely ignored just how middling MLB expansion has gone, which is an indicator that finding a loyal market for a team is really hard to do and takes decades, not years. The last four expansion teams are Arizona, Colorado, Miami, and Tampa. Colorado is the only one of the four that doesn't live in the bottom half of MLB attendance most years. Even Arizona, which isn't regarded as a failure like the Florida teams, doesn't draw particularly well, doubly so once you consider that Phoenix is one of the largest metro areas in the country.