Rubio staying in the race after March 1 was an enormous error on his part that will hurt both himself and the chances of toppling Trump. If the polls are anywhere close to accurate, and that is not a given at all this year, Rubio is about to get beaten badly in his home state. That seems to me to be a career-ender politically.
But compounding that is the fact that Rubio has prevented Cruz and, sometimes, possibly Kasich from getting more delegates which have instead gone to Trump. As an example, without Rubio, Cruz would have captured all of Idaho's delegates by getting over 50%.
Rubio had some bargaining power with Cruz. He could have been the running mate or received a cabinet position.
But compounding that is the fact that Rubio has prevented Cruz and, sometimes, possibly Kasich from getting more delegates which have instead gone to Trump. As an example, without Rubio, Cruz would have captured all of Idaho's delegates by getting over 50%.
Rubio had some bargaining power with Cruz. He could have been the running mate or received a cabinet position.

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