Hate to throw another wrench into the mix but I got the same 2008 g37s 6MT and this sounds very similar to what happened to my G.

A couple of years after I got my G I was driving and it just died similar to what you are describing. I was on the side of the road and tried so many times and it wouldn't start.
Still under extended warranty I ended up towing my G to the dealer.
As it turns out the dealer ended up replacing the galley gasket to fix the issue and the CSC was also replaced
There were no codes showing when the dealer checked for any codes in the system.

Having said all that......hopefully this is not the issue you are having but just wanted to share my experience with a similar issue.

anyways, hope your issue get resolved.