The Daily Beast article puts the best face on the possibility of Trump leaving. They say that the phrase in the Republican rules committee which says:
the Republican National Committee is hereby authorized and empowered to fill any and all vacancies which may occur by reason of death, declination, or otherwise of the Republican candidate for President of the United States
, because the word "otherwise" is in there, means the Republican Party can remove Trump from the nomination for being unfit, even against his will. I am not so sure. The article says that if Trump fights and goes to litigation, it will be difficult. I agree. About a quarter of the states require those electors in primary elections must vote for who was on the ballot, and if Trump is taken down after the nomination, those states will likely say that Trump's firing was a way around state law and prevent the new replacement candidate from appearing on the ballot in that state.
In short, unless Trump resigns, the Republicans are stuck with him no matter how much he stinks up the place during the campaign.