I think if you got low enough to scrape the muffler, you would know it. I would think the bag would touch down first though.
Think new bike, first time on a track, about a 170 degree right turn, off camber, slight down hill, heading toward a up hill climb with a hard left hander, focusing on a drill experience. Something else he did was enter the corner way too early, which set up the potential for a really bad experience, which fortunately didnt happen. Purt near full compression on suspension, exagerated angle and rapid application of brake led to the touch down. If he had chosen a better entry point and better body position his speed woulda been fine, instead he chose an early apex vs a late apex and he had a mild panic attack, hence the brakes. He had no idea he touched, but the scrapes were all the evidence he needed. And BTW, bags were off for that session.