In a typical election, a candidate in his position would be done; but this election isn't typical.
First, he needs to unify the party. Recent polls, especially the ones in red states (eg Georgia, Arizona, and Utah), suggests that millions who voted for Romney and McCain are not supporting Trump right now. To achieve this purpose, he may need to campaign with some establishment names and use his running mate more aggressively. He won't get all of the Romney and McCain voters, as neither Romney nor McCain is supporting him, but he needs at least 90%.
Secondly, once he gets the Romney and McCain voters, the race should tighten. Thereafter, he has to run a professional campaign to get independents and crossover Democrats. No more gaffes, and more emphasis on his moderate or left wing positions (ie trade).
If Trump were capable of running a professional, gaffe-free, reasonable campaign, he wouldn't be in the position he is in.
I think Trump can maybe still win, but he needs Hillary to screw up badly or for outside events to change the race. Absent those circumstances, I don't know how he has a path.