At this point, the only way Trump runs as independent is if he wins the primary and then gets disqualified by the party leadership or something. He doesn't have to consider being an independent, he's got the Republicans firmly gripped by their smooth old man balls.
It's not quite a foregone conclusion. The states that hold republican primaries between the 1st and 14th of march award their delegates proportionally (like the democrats do for all states). That means that the divided field wont help Trump for the next 15 days. If he wins 35% of the vote on Super Tuesday that leaves 65% of the vote that goes to delegates who can block his nomination at the party convention.
So suppose that in the next two weeks, Trump takes 35% of the vote on average. That means there are 608 non-trump delegates. Add to this some of the 150 unpledged republican delegates (who are probably very much in the Rubio camp). 1237 are needed to force a contested convention so not-trump needs to win 450 delegates in the winner takes all states to get a contested convention. There are 1213 delegates to win in the winner take all states so they would need to win 38% of those. Just a few victories would do it and some states he might lose are, Ohio, California, Indiana, Pennsylvania, Wisconsin and North Carolina. So Trump could in fact win 40 states and still wind up with a contested convention. I really, really suspect that the GOP would side with Rubio or a dark horse candidate (or Kasich!).
I'm not saying it's certain, I'm saying that a plurality doesn't win you the nomination like a majority does. And Trump losing after a contested convention seems like exactly the sort of thing that would make him go independent. Which the GOP might be okay with because it's less damaging to their brand.