An external acquirer would almost have to build from scratch after absorbing all the legacy costs and run the risk of inheriting Sprint's bad business decision culture or spending an enormous sum building out a new team. Of course, they'd still have to support the old and new setups at the same time for awhile as the new stuff was built out. The ROI would have been decades at best.
With a merger with another telecom, people can be migrated over already existing infrastructure (with some upgrades to deal with new traffic) and have sprint's old spectrum slowly merged into the existing infra.
I'm oversimplifying of course, but one gets the idea.
That never would have happened without Softbank buying them however.
But it is historically far and away the most likely one.
Allowing an anti-competitive merger simply because the alternatives for Sprint shareholders were bad is a bailout by any other name.
Could things have been done differently? Sure. A condition of the merger could have been guaranteeing MVNO access or selling off a portion of the spectrum (maybe that happened).
But T-Mobile, combined with Sprint, went from being a distant competitor in subscriber numbers competitive. If sprint was "sold off" separately, T-mobile would most likely eventually run out of steam and end up like Sprint. They just wouldn't have the number of subscribers to amortize costs down the way AT&T and Verizon could.
Keeping struggling, small players going somehow would likely of only delayed the inevitable.
Unless you can show me how a cellular company that and backed itself into a technological dead end (and built up enormous debt during said process that sapped most of the money it earned to service) and needed quite possibly multi-tens of billions to even catch up to the others, you're not really adding to any conversation. If it was possible, business-people with more money and brains than either of us would have leapt at the opportunity.
The only alternative I can possibly think of is taxpayers ponying up - but that would in the end mean that consumers would "pay" indirectly, to say nothing of the moral hazard costs of government bailing out private businesses (works so well in the financial industry, doesn't it?).
Being acquired by a competitor wasn’t their only exit option, and pretty much anything else would’ve resulted in more competition.