In my view Trump's chances of re-election have probably risen by lot just lately.
I see two ways a Trump-Sanders general election can go. Both strongly favor Trump. I'll describe them both briefly.
Capitalism versus socialism.
I know socialism is all the rage among people who have never voted. I am unimpressed. Anyone older than 45 is much more likely to vote. They also remember the terror and atrocities of "people's" "democratic" socialist states.
No one in this group can honestly be convinced by the facile added adjective "democratic." Indeed, using that adjective is precisely what the Soviet Union did. Doing it yourself doesn't actually make you sound more democratic. Wearing it on your sleeve makes you more Soviet.
Capitalism versus socialism is already a popular theme at Trump campaign rallies, and with good reason. It's a winning theme. It doesn't matter that Trump is offering fake crony capitalism. It doesn't matter that his actual policies resemble those of a corporatist mercantilism. At least he's not a democratic socialist.
Honey versus vinegar.
Trump's campaign will often be relentlessly positive about America. This will easily prove the more popular message, exactly as Reagan beat both Carter and Mondale. When given the choice between pride in the nation--and hand-wringing about how we are all irredeemable racists, and how a nation full of billionaires is really a nation full of failures--people will take optimism every time. You get more flies with honey than you do with vinegar.