I'd definitely pick Dolly Parton, just to see DG say "WTF, I thought you were busy for the next two years?! Are you free say, um, NOW?!" Then watch the awkward encounter that proceeds between the two as they try to come up with something together. For the other artist, it'd have to be Willie Nelson, so he could be the peacemaker (He's worked with Dolly before, and I'm sure he would have something to help mellow everyone out.)
And, even though I'm not a fan of country, it would be awesome. I'm sure they'd come up with something. And, even if they didn't, I'm sure we'd all have a blast.
If you were to take the stuck elevator out of the scenario, my answer would be totally different! ;)