So the power from the optical system is spread over the retina by the MEMS mirrors. What happens if the laser stays on and one or both of the scanners stops?
MEMS mirrors have built-in angle sensors, and when these report that there's irregular or no detected movement in one or both directions, the lasers are turned off.
The lasers in a MEMS mirror near-eye display operate in the microwatt range. Low power laser pointers operate in the milliwatt range, and the safety mechanism for those is that your eyelid is expected to shut to block off the laser in less than a second. Therefore, you have more time to shut your eyelids or remove your eye from the MEMS mirror display if there's a failure and the lasers fail to shut off.
It is an inherent danger in the system, but I would be interested in reading a full risk analysis on this type of system. Industrial processes always have risk analysis and avoidance, with failsafe for all possible failure modes being desired. I wonder what kind of hardware failsafes you could put into this. You never, under any circumstances, want to burn someone's eye. But you also don't want someone's expensive toy to brick itself because they jumped with it on.