From past experience (July skiing at Mammoth in 7 prior seasons) I can make some educated guesses. The core, easily accessed runs from the top, Climax, Cornice and the Drop Outs/Wipe Outs should be fine for July 1-4. Hangman's is al;so accessible and should ski fine until its throat melts out, which this year should be later than the July 1-4 holiday. Outlying runs are more problematic. The key issue is suncupping in areas that aren't skied very much. This is one reason it's great that Mammoth runs daily and not just on weekends.
With outer areas the runs may have tons of snow but the approaches to them burn off. YOU may be fine with hiking 5 minutes over scree to access a run, but 95% of skiers aren't. And if enough people aren't doing it, the suncupping will progress, the snow will degrade and become not worth skiing.
Skyline was already marginal over Memorial Day and Roadrunner is likely melted out now too. The approach from the very top of the Paranoids had also lost its snow by Memorial Day. Thus the only access to Scotty's and beyond is via Wipe Out 2/Hump, then traversing to skier's left. Typically there will be a couple of nice skier packed lines in Monument and Paranoid 1, but nothing beyond that. With this year's snowpack maybe you can continue that traverse out to P2, P3 and Philippe's for a while longer than usual, but I think it's close call whether it will be any good beyond P1 by July 1.
The long traverse over to Dave's usually burns off during the early June gondola maintenance period. I have no recollection of ever skiing Dave's in July. Access to Huevos without hiking is very unlikely IMHO; thus I suspect its snow won't be good by July either.
Based on 2011 I'm optimistic about the July 1-4 holiday. Stump should be open, which opens more lower mountain salted groomers plus makes the chair 5 terrain accessible with exit via Comeback Trail to chair 2. St. Anton should be open, allowing long top to bottom runs skier's left of chair 23. And the race course runs under chair 1 usually stay in good shape midday when the other lower groomers get too sticky.
The skiing gets more limited after St. Anton and chair 2 close. This is the situation on most July 4 closing weekends but will occur a week or two into July this year. And finally the lower mountain will burn out, leaving just chair 3 and the upper gondola. Later in July I would expect just Cornice, Climax, Saddle Bowl and maybe face of 3 open. That's still worth getting a ski day in but perhaps not multiple days. But I'll still go up there to check it out as there are many other things to do in the area.
If Saddle Bowl gets to be a narrow WROD like the closing last year with Cornice being the only run open with any elbow room, that's the point it might not be worth the trip IMHO. But I'm guessing Mammoth needs more than that to run the race camps, which is why they are staying open into August.
