1. Actual total radio failures (aircraft equipment) are rare, I never had one over the last 30 years.
2. On our long haul fleet we already have the satcom system and that is used extensively for company comms and, sometimes, for atc ops when no datalink is available and hf is unusable due to atmosferic conditions.
3. Yes, when all of the above is not applicable then your mobile is the last resort.