And, something like Trump getting Rubio and/or Carson to throw to him would immensely help... that changes those delegates.
After the delegates cast their first votes and if nobody receives 50 plus 1 percent then the delegates are no longer bound to their previous candidate and they will be free to vote for whoever they want. A candidate does not own the votes but can recommend to the delegates their desire for them to vote for Trump or whoever.
It could turn into one hell of a fight with trump getting PO’d and run off to a third party. The rules are the rules and the owners of the game wrote them.