There are at least three reasons the RNC won’t cut Trump loose (at least not anytime soon):
1) The RNC is raising a lot of money with Trump now, especially via small-dollar fundraising. The fear is that if the RNC cuts Trump loose, Trump cuts it loose in turn and that the fundraising dries up and there are no resources to re-allocate to down-ballot races.
2) If the RNC gives up on Trump, it will be a blow to Trump and he will drop further. The worry is that if he begins to trail Hillary by, say, 12 points, there is going to be no saving down-ballot races regardless.
3) It’s not 1996, when the party managed to pull this off. My understanding is that Bob Dole went along with the strategy to try to save the senate in 1996, meaning he kept doing all the work to boost the party. It’s impossible to imagine Trump having this attitude. And related to point 1), in 1996, the party could easily raise soft money from corporations and spend it on advertising–that’s no longer the case.
So, for now, it’s going to be the status quo and hoping for the best.