Even if Trump were polling at 40%, that leaves 60% to go to an opponent for the nomination.
40% is pretty much a lock statistically.
As the other candidates drop out, they’d have to go 80-20 to the No. 2 guy in order to tie Trump. That won’t happen. Other things could change the dynamic, most likely, but if Trump is polling at 40% closer to primary day, he’ll win the state no matter who drops out.