A code can possibly tell them its a loose connection?
Well no, not exactly.
But a "loss of communication" error could be a loose, damaged, or corroded connector within the SIR system. It could be something more significant as well.
As far as talking with your dealer, goodwill repairs are designed to "affect quality repairs and meet reasonable and rational customer expectations" under special circumstances. In this case, the SIR system is a critical item of vehicle safety and a customer should reasonably expect it to operate properly for a significant time beyond the bumper-to-bumper warranty period, much less just 3,000 miles beyond it.
It is a total gray area and is strictly up to the dealer, but the repair has to be justified to GM in order for the dealer to get reimbursed. I've never had to plead a case like this to my dealer, so I really don't have any other advice, sorry. Good luck.