This will depend on what happens during the primaries. For instance, suppose that Florida Sen. Marco Rubio secures enough delegates to win the nomination (1,237) as well as a majority in 20 different states, while Texas Sen. Ted Cruz is second in the delegate count and holds a majority in 10 states. In that scenario, the RNC might make the threshold 15 states, thus disqualifying Cruz and avoiding a convention where a large number of Republicans vote against their nominee. Or imagine a scenario when no candidate has the crossed the 1,237 threshold heading into the convention but each of the leading candidates – say, Rubio, Cruz, New Jersey Gov. Chris Christie and Donald Trump – has a majority of delegates in seven states. Realizing that a floor fight is inevitable, the RNC could decide that the best thing to do is reduce the state minimum to seven, thus managing the fight in a way that gives each of the leading factions a voice and decreases the risk of anyone bolting the party.
These scenarios are not meant to be predictive or even realistic – they just illustrate some of the ways the RNC might respond to different primary outcomes. The bottom line is that Rule 40 is highly unlikely to stand between the leading GOP candidate and the nomination.