Fine, swap an impossible reality for a slightly-less-impossible reality. I feel just as confident saying "a third-party will not keep a candidate from winning the electoral college" as I do saying "a third-party candidate will not win the election." Third-party candidates do not siphon votes equally from the two major parties, they typically just make it easier for one to beat the other. I think it more likely that a third-party candidate could get as much as 30% of the popular vote without winning a single electoral vote.