1. President Pence would be good. He could appeal to the traditional Republicans as well as the “basket of deplorables” who put Trump in office.
2. To remove Trump from office would require much Republican support, which would alienate the Trump-base and result in Warren or Sanders getting elected. To win a national election the traditional Republicans (“Country club” or “Wall Street” or “Chamber of Commerce” flavor) need the populist base. Anything that alienated the “deplorables” costs the Republicans.