Two-thirds continue to vote for someone else. The question is, will these votes coalesce behind someone else, or go to Trump? I expect that they will gravitate to someone else.
I just did the math:
If we just take Republican voters (your best scenario, with the independents all gone), and if Kasich goes, Bush goes, Fiorina goes, Christi goes (and he's going), and all their votes go straight to Rubio:
That total number is 37 percent to Trump's 35, only over Trump by 2 points.
Considering how unlikely such a scenario is to begin with (Christi actually does appeal to conservatives, and won 4 percent of "very conservative" and 9 percent of "somewhat conservative", and if almost the entire field drops out, we have to assume that Trump's numbers do not increase in any way), Trump is doing very well indeed.