That seems really impractical. Even third parties and write-ins made up 40% of the vote, it would still be impossible for either Trump or Clinton to get less than 30%.
If Johnson and McMullin both strengthen as a result of Trump's implosion, the following is not inconceivable:
Trump 29%
Clinton 28%
Johnson 22%
McMullin 17%
Stein 3%
Others 1%
Before this latest problem, Clinton was already polling below 30% in Utah, Trump had been polling the mid- to upper-30's and both Johnson and McMullin had been polling above 10%.
Utah's developing into a four-way race, which is of course, the only way the winner could end up with less than 30% of the vote.