Nobody can plausibly overtake Trump in the delegate count. In principle, a convention could block Trump from getting the nomination anyway. Doing so would unleash chaos, and potentially fracture the Republican Party beyond repair. Might some actors prefer a party rebuilt from scratch? Maybe, but they won't do it.
The key thing to remember here is that a party is, among other things, a vehicle for career advancement. People who have positions of influence within the Republican Party today are achieving a primary goal. To tear the party down and rebuild would be to undermine their own career advancement.
Think of a business. Consider the position of a bunch of VPs of various functions. They may not like the current CEO. They may not like the person set to become CEO, but they have no incentive to break up the company in the hope that they can achieve similar positions in whatever rises from the ashes.
This is what we must remember about party functionaries. Existing Members of Congress, Governors, state legislators and other muckety-mucks need a party system to maintain their positions, and possibly advance. The strongest incentives to destroy an institution are always among those who don't benefit from it. The people who could try to block Trump, then, are actually the ones who would be hurt most by doing so.
That is why we are seeing so little real movement to block Trump, as demonstrated by this nice piece by Andrew Prokop.