First there was "low energy" Jeb, then "Little Marco," and still "Lyin' Ted". This weekend Trump has rolled out his damning branding of Clinton as "Crooked Hillary," which brings up her long history of corruption as well as the rigged nomination process. She'll sell out the American people to further line her pockets, and she could only receive the nomination by influencing / bribing the superdelegates rather than the actual voters.
He has yet to brand Sanders with an attack on his character, you could argue because he's not much of a threat, but more likely because that's a bridge he doesn't want to... bern. Sure, he tosses out the "socialist slash communist" line, but anyone who can't tell he's just ribbing him is a humorless nerd. It's like one buddy teasing another for being a "chubby-chaser". And "socialist" only goes to his ideology, not some fatal flaw of his personality.
Whether or not Trump would go as far as offering Bernie the VP slot, he'd have to be crazy not to include him somewhere in his administration, and to broadcast that promise in order to draw in the Sanders supporters (the normal majority of them, not the fringe leftoids).
Keep him away from a position where he could do damage, like single-payer healthcare or free college for all. Maybe head of the Federal Trade Commission, though, restoring the agency to its original function as trust-buster rather than milquetoast "consumer protection" stuff.
If Trump is going to give a list of 10-12 potential appointees to the Supreme Court, why not do likewise for other key positions, to let voters know concretely what kind of administration they'd be choosing. It would also present a challenge to Crooked Hillary:
"So who would you put at the head of the FTC? Some party hack who gave a lot of money to your Clinton Foundation? -- which is a total scam, by the way -- You see, folks, that's all she is, is crooked. I'm going to put Bernie Sanders in charge of trust-busting, and the media monopoly and Wall Street are not going to have an easy time, that I can tell you. Hey, folks, would there be any President more unifying than Trump?"