I would advise that, unless you are 100% certain about your resolve and strength against temptation and portion-non-control, avoid the buffets like the plague. I'm not one to usually suggest people to run away from any challenge, to find a way to live through it instead, but you would have to be made of steel to survive those seductive horrors.
I looked up "Las Vegas Healthy Dining" in Google (My Best Friend tm) and came up with this address:
http://cityguide.aol.com/lasvegas/besthealthydining/
I don't endorse anything there, as I haven't eaten at any of the places listed, but it might be a start? There were some other promising-looking pages, you might want to replicate my search.
Otherwise, do you know if your accomodations will have a fridge? Even if you can't cook, you can eat pretty well- sandwiches, salads, fruit, veggies, cold drinks, etc. That might be a good option if you don't want to eat out for every meal. And, you can always search for the most "traditional" restaurants you can find and just order the way you would at home- search for the healthiest things on the menu and be prepared to not eat everything if the portions are too big.
Otherwise, if you are made of steel- most of the buffets I have been to offer plenty of healthy options. I just wish they were in a different building then the "
others".
Good Luck! I hope you find some time for fun as well as business.