Now come on --does Trump NEED any support from the other candidates who drop out? Ofm course not.
Well, yes, he needs help. People need to realize that Trump has about 40% of support from registered voters. Note: Not registered Republican voters. Not "likely voters". Not likely Republican primary voters. Just overall voters.
Trump has to win Republican PRIMARIES. That takes the votes of registered Republicans that will vote in primary elections. Right now he doesn't have a majority of these voters, he's got about 36% of them.
http://projects.fivethirtyeight.com/election-2016/national-primary-polls/republican/
As other candidates drop out, their supporters will be going to Rubio and Cruz mainly, because once Super Tuesday is over, that's the only other two that will still be in the running and because Trump has insulted everybody else. Then the polls will tighten, it could even be a three way virtual tie with all three in the 30%-35% range.
Don't forget about states that have open primaries or allow party crossover voting. Democrats can vote for Republicans in these primaries and if they do they would vote for a candidate that they feel would be the weaker Republican candidate. They probably perceive that Cruz is that candidate.