If Sprint ever wants to buy T-Mobile, one of them is going to have to fail

Sprint(s s) may have given up on buying T-Mobile this year, but wireless industry analyst Chetan Sharma believes it’s only a matter of time before the two renew their courtship. A merged Sprint-T-Mobile(s tmus) is inevitable, according to Sharma, but if the two want to consolidate sooner rather than later, T-Mobile will have to stop performing so damn well.

“The path to the eventual marriage might be tortuous and could involve detours but the market dynamics are likely to force them down the aisle,” Sharma told me in an email interview.

Sprint’s timing was horrible this year because a rejuvenated T-Mobile, quarter after quarter, refuted Sprint’s core justification for merger. Sprint chairman and SoftBank CEO Masayoshi Son argued that smaller carriers needed scale to compete against the enormous might of AT&T(s t) and Verizon(s vz) — only by becoming a mega-carrier itself could Sprint level the market.

Source: Chetan Sharma Consulting
Source: Chetan Sharma Consulting

But for the last 16 months, the country’s smallest nationwide operator has been on a tear. It’s led the U.S. mobile market in subscriber growth, luring postpaid smartphone subscribers away from the other three and stealing a good chunk of Sprint’s own prepaid customer base.

In just five quarters, T-Mobile has managed to reclaim nearly all of the postpaid losses during its 15 quarters of decline between 2009 and 2013, Sharma points out in in his newest U.S. Mobile Market Update. By the end of the third quarter, T-Mobile will have fully recovered, erasing that dark period of its history, Sharma said.

In most of those recent quarters T-Mobile reported net losses, raising the question whether its new Uncarrier strategy was sustainable. But regulators were already wary of more consolidation among the Big Four. T-Mobile’s runaway success provided daily evidence that consolidation wasn’t necessary for smaller carriers to compete. Maybe what Sprint needed wasn’t scale, but rather an outspoken and aggressive CEO like John Legere to put it on the right path.

“To be considered a player requiring some regulatory assistance, [T-Mobile] has to probably get back to those levels of losing 300-400K subs every quarter,” Sharma told me.

Source: Chetan Sharma Consulting
Source: Chetan Sharma Consulting

Another possibility is that Sprint’s decline continues under new CEO Marcelo Claure and is lapped by T-Mobile (it’s only 4 million subscribers shy of becoming the No. 3 U.S. carrier). The roles might then become reversed, with T-Mobile buying out a struggling Sprint, Sharma said.

“My long-term thesis is that these two entities will get together one way or another but unlikely under current administration,” Sharma said, but he added there may be many other deals along the way as T-Mobile’s controlling stakeholder Deutsche Telekom is eager to divest. T-Mobile may become the property of another foreign owner (France’s Iliad has already made a bid) before it merges with Sprint, Sharma said.

So Claure appears to be a rather precarious position. He’s been tasked with rejuvenating an ailing Sprint. But Son, Claure’s boss, obviously still has ambitions to buy T-Mobile. If Son really wants to get the two together, Sprint or both companies will need to perform badly.