In the 60's neither Disney or Warner Bros had the means to buy each other out same for the 70's.
Early to mid 80's Warner could have bought Disney but only by selling off a good chunk of Disney's assets, after Disney righted itself then Disney could have bought Warner Bros by doing the same thing with Warner's assets.
Now if Disney buys Warmers it would have to divest some of the Warner's assets like DC comics in order to overcome anti-trust objections just like Disney had to sell the local Fox Sports channels to get approval to buy 20th Century Fox.