In truth Vince is often unjustly vilified when discussing this era. He didn't do anything illegal, he was simply being a shrewd businessman. Had any or all of the other promotions adversely affected by his actions gotten their act together and emulated McMahon's approach it's entirely possible the WWF expansion would have faltered and ultimately failed. A new top dog could have risen to prominence.
One thing I don't think would ever have happened is the status quo remaining. The territories were doomed.
Cable television was one of the main tools the WWF used to help grow its audience. They succeeded in part because Vince was the first wrestling promoter to seize on what cable offered. He struck marketing deals and ventured into areas that his TV show had headed into first. Had another company done this they would have been number one.
To say Vince and the WWF put the territories out of business is incorrect. He put companies out of business, just as he did two decades later when he contributed to the overall failure and closure of World Championship Wrestling. Vince did not completely wipe out non-WWF wrestling. He made it impossible for the larger companies to keep going, through a mixture of encroaching on "their" turf and signing wrestlers who were available.
Other, smaller promotions rose to take the place of the fallen giants. ECW was essentially a regional promotion. It was more akin the to territories' regional model than the WWF's national one. It's just that the Extreme outfit's region was a little bigger, taking in everything from New York City to Florida. A territory would have run shows throughout three or four states at most whereas ECW ventured up and down the East Coast, mainly running shows in Philadelphia and NYC because they were heavily populated cities with a proven track record of having passionate wrestling fans.
ECW was essentially the most prominent territory of the 90s. Jerry Lawler's Memphis league (a survivor of the McMahon expansion), Jim Cornette's Smokey Mountain Wrestling, Heartland Championship Wrestling and LA’s XPW were others. The territories didn't go away, the companies that they consisted of just changed.
They became the indies. Thirty years ago a wrestler starting out would have been taught the ropes and then started working their local territory. After a few years they would generally move on to pastures new. That would happen every few years unless they happened to catch on as a top babyface somewhere, in which case they could stay put. There was such an abundance of wrestling leagues that a wrestler could have a long and prosperous career without exhausting their options.
Modern wrestlers will learn the ropes at a wrestling school, most of which are attached to a promotion. That allows young wrestlers to start getting experience early in their careers. Generally speaking a modern wrestler will work for one or two local outfits, with some being lucky enough to get work with the larger companies like ROH, Dragon Gate USA, CZW, CHIKARA Pro and EVOLVE.
The guys you get in CHIKARA would not necessarily have succeeded in the territories of the 1970s
Finding a wrestler who only has experience with one of these companies is unlikely. Once they're good enough for one they will likely get regular work with them all and wrestle for some or all concurrently.
Will Vince McMahon and WWE put these companies out of business? I think it would be a much tougher challenge. Modern companies have shown they are just as capable as WWE at getting cable TV deals, with YouTube and internet pay-per-view providers being ideal tools to reach a global fan base. Fans have also become more sophisticated in their tastes, not just being happy to watch whatever match, story or character Vince and company happen to be pushing but actively seeking out companies that offer something different, whether that’s the humour of CHIKARA, the young guns of DG USA and EVOLVE, or the stiff style of Ring of Honor.
WWE still signs people from the independent system and it still thrives. CM Punk, Bryan 'Daniel Bryan' Danielson, Antonio Cesaro, Kassius Ohno, Dean Ambrose, and Seth Rollins were all considered standouts of the independent circuit and all now work for WWE. Ryback and John Cena started out there too, before being placed into the sports entertainment farm system. When a star leaves the indies another rises to take their place, just as the indies did with the territories started disappearing. It's what's always happened in wrestling. It always will.