I think that he really needs to hold his ground in the Republican race for a number of reasons.
If, he does not get the Republican nomination, I believe he must then make the choice; I will respect his choice either way.
This 72 year old man is running himself ragged on the campaign trail for US. He even states as much publicly that he will do what the people behind him want him to do... run hard and run to win. He KNOWS who his employer is.