The outage took out at least some of their aviation services. If they are unable to update routes and IFR approach procedures then lives could indeed be at risk.
Not quite. The onus is on the pilots to never fly with out-of-date navigation information (it's actually illegal), so if they can't get that from Garmin, they'd just have to get it from somewhere else instead. Garmin's data services being unavailable isn't endangering anyone.
They don't. Garmin's cloud services supply map/chart data updates and backend services for their mobile app (which is separate from installed avionics) to support flight planning functionality.