The Braves signed a 20 year deal in 2008 that was well below their market value in 2008.
They are getting a big revenue boost out of the new deal whether the television deals are still expanding or not.
There is no particular reason to believe that tv money will be going backward. I don't think we've seen examples of that. If anything, stable TV money would be a benefit to Atlanta as you are most vulnerable just after you've signed the deal. Ask the SEC, which ended up expanding to create new content due to a signing a long deal that turned out to not be market setting for very long.