Trump... change his image? He is a narcissist. He'd never do that.
I feel I would really like to see him disappear from our political scene but he is stubborn man with kind of consistently racist line he could end up being viable to an electorate that the Republicans keep trimming of minorities with all kinds of state laws and purge efforts... and of course there are always the "voting" machines.
We need to understand that our electoral system is broken and it does not reflect the actual will of a majority of the people. In such an environment, electable can happen where it shouldn't.
No, Trump is so unelectable and would cause large losses in the House and Senate (or at least as big as they can be with this polarized nation). He has said at least three or four things that would have derailed any other candidate. David Duke is probably thinking "I was a man before my time" right now.
Trump has insulted Hispanics, women, and Muslims. And while Muslims only represent 1 or 2% of the nation, women are a bit higher at about 54%. Trump can't take any minority by more than 25%, at most. If he can't win half the women and do decently among the minorities, he can't win. And as things stand, he has been so insulting, he'll take the Senate and possibly the House down with him, easily. You can only do so much with the angry white asshole demographic.