In July, in the high snow year, a friend and I made that error and stayed right, going down a gentle slab chute rather than staying on the partially snow- covered trail above Mirror Lake. We figured out our error quickly enough, but didn't backtrack -- it was morning and we had both good weather and good light. Instead, we figured out a safe way down that required a creek crossing and dropped us below Mirror Lake just above the switchbacks leading to Outpost. My friend, who was leading, was initially headed for the cliffs above Outpost. Having been on the trail before, and consulting topo, I warned her off and we turned left/north before the cliffs to drop down to the creek (there is one safe place to do this). Pretty sure we hooked up with a shortcut/section of the old trail during this detour.