I don't think you necessarily need a case to benefit: I don't use a case but slipped on a marble floor once and dropped the phone straight onto the floor, causing it to bounce a few times. The rim of the glass
dented (what looks to be a thin plastic coating on the side of the glass?) but nothing shattered.
In any case, IIRC, speculation is that only the screen side of the iPhone uses Gorilla glass, but I'm not sure if that's changed with recent generations. But even without Gorilla glass, you can still use "standard" toughened glass that, correctly mounted, should never shatter just from the sort of thermal shock described in the article.