Betting on the death of T-Mobile is like taking candy from a baby. And that has nothing to do with the AT&T acquisition. Because it has been evident for years that due to the network technology issues mentioned in the article, T*Mobile has been a walking corpse for years.
The only hope for T*Mobile has been to be acquired by AT&T because AT&T is the only company that has any significant degree of network compatibility. Sprint's goal in opposing the merger is simple - to kill T*Mobile so that T*Mobile customers need to switch to other carriers. Sprint has no interest in acquiring any of T*Mobile's physical assets, and Sprint doesn't have the capital to upgrade them anyway.
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Also, relevant to the article, T*Mobile is essentially abandoning the mass market anyway and ceasing to compete with AT&T, Verizon and Sprint. They simply can't compete there. Instead they are moving downscale, emphasizing cheap programs, where their competition is outfits like Virgin Mobile and MetroPCS. And if you've seen recent Virgin Mobil ads they've started directly targeting T*Mobile customers. (BTW - Vifgin Mobil is also Sprint.)