Ignition Module problems of the 2008 Buick Enclave

While driving engine turned off on 4 separate occasions in the past 2 weeks. Never any warning lights or check engine light just engine turns off suddenly. The first time I was driving on a busy city road middle lane at 25-45 m/hr. No power steering or brakes. Unable to restart I was able to push into a parking lot and call for help, it was towed to my mechanic who said rollover switch tripped. 2 days later engine turned off again while exiting highway at the same speed but was able to restart in neural after a min stopped, I drove it straight to my mechanic who reset computer and drove it around for 3 days unable to diagnose problem on computer. 2 days later while driving 45 m/hr engine turned off again. I was on a small decline 2 lane busy road and able to restart in neutral position. A few times in the past few weeks vehicle would not start after parked for a few hours but would start in neural eventually after many attempts, 12/24/2016 while driving on a busy 2 lane street in town engine stopped again no power steering or brakes at 20 m/hr. Unable to restart and passengers had to get out of my Buick and push into nearest parking lot. Unable to restart, towed on 12/26/2016 to local Buick dealership to be diagnosed by a certified dealership per the suggestion of Buick USA. They can not find a problem per computer diagnosis and are trying to tell me there is some water damage behind dash on fuse block that will cost me thousands of dollars to repair but no guarantee that that is the problem I have never had any problems with lights, radio , ac or any other electrical issues that would lead me to believe that the fuse block has water damage. . Per gm forums there are many issues with ignition switches or ignition control module . Could this be the problem . My engine turning off while driving is a real safety concern and how do I resolve this problem.