It could be boring. This scenario would play out if Clinton decides that she needs to work on making the positive case for herself more than anything else and Trump calculates that calm, cool, and non-combative is the best way for him to go.
Trump is more prepared than anyone expects. It would be a clever ploy if the Trump team has actually done a much better job of briefing him up than they’ve let on (although usually a candidate who is learning things begins dropping better-informed riffs in interviews and at events).