I would be curious to know the time span between when they worked on your flat and your wheel came off. Was it the same wheel? Might be facts to help your case with the dealership. Sounds like you talked to most of the right folks already. The only thing left is to find out who your regions factory rep is and contact them. If all else fails, turn it into your insurance.
And yes, as everybody has said, it's a good habit to get into to check your lugs. I check mine after anybody works on tires/brakes/bearings. Also check before most trips. But saying that, in 30 years I've never found any 1 lug loose enough to cause me concern, much less cause all the lugs to break. So I think somebody at your dealership didn't do their job properly.
As for all the folks placing blame on you for going 70mph.... PPHHHHTTTT!!!! Didn't have a dang thing to do with loose lug nuts or the dealership not reimbursing you. But as you know from these threads, traveling over 65 on STs causes male pattern baldness and global weather changes
Keep hounding the dealership with facts and receipts for damages. You would think they would help out just for customer good will!!! Good luck, and let us know if you get any action on this.
Scott and Liz - Southern NM
2012 Wildcat Sterling 32RL - w/level up (best option ever)
2007 Chevy 2500HD 4dr short bed Duramax w/allison
Reese Fifth Airborne air ride king pin coupler with Sidewinder