Apple was never going to beat the WinTel hegemony in the corporate sector as long as it continued it's closed approach. Corporations want things their way, not the Steve way which is why Microsoft have that area sewn up. They know how to do business.

It's hard to know whether the clones would have made any real impact if they'd be left alone. They still relied on Apple for the OS and the PowerPC chip was never as fast as Apple tried to market it as. The move to Intel was inevitable and probably should have happened a lot sooner (like when they were developing Rhapsody). Computer Chronicles have an episode that covers not just the clones but Copland too. Well worth a look. Certainly Apple were in a crisis at that time. The clones were building better machines for less money because they weren't tied to using proprietary components. Another case of the closed ecosystem coming back to bite you on the ass.

NeXT pretty much was a failure. It never made a profit and while the hardware looked funky and the OS was way ahead of it's time, it never caught on the way it was predicted to.