As I recall (although it is only a recollection, so if someone's got better evidence than my unreliable memory I stand corrected), what drove the triumph of the PC was not that it contained an 8088, but the software available for it and the ease with which third parties could make compatible hardware (and indeed, clone the whole thing).
I suspect (but cannot prove) that both of those could still have happened if they'd gone with the MC68000.
I'd argue for 'open' hardware platform more than anything. Take a look at other personal computers of the time, within an order of (or two) magnitude price up or down, like Mac, Amiga, Atari, SUN, HP(UX), and SGI. They all had great(er) software and hardware and more advanced OS' and features, but got trumped quickly. On the software side, PC had business productivity from the start which could be used as an argument on the software front (Lotus 1-2-3, namely).
To cite "Triumph of the Nerds" again. There were several things that came together to make it possible. IBM's support for it was pretty essential, their bureaucracy being incompatible with a fast changing market leading to them outsource all of the components, and the simplicity of the system making it easy to reverse engineer.
I suspect (but cannot prove) that both of those could still have happened if they'd gone with the MC68000.