Well no, people will just stay with Windows 7 in that case.It's a huge gamble, if Metro fails (and it looks that way), it could take down their OS business with them.
I think the criticism of Win 8 on desktop machines is overblown but the positive noises the Lenovo is making on Windows 8 shows that the O/S is pretty much directly aimed at tablet/laptop hybrids seeking to compete with tablets and designed to be attractive to app developers. If that is the next big growth segment than Windows 8 will do gangbusters business (and MS will have anticipated the market Apple style rather than follow along with a me-too product). If people on enterprise and/or desktop stick with 7 then I don't think MS would be particularly unhappy about that.