There will never be single pilot airliners. The pilot is either a critical system or he/she is not. If they are, they will have a redundancy onboard, just like every other critical system. If they are not, there is no need for them at all. If the airplane can be designed to safely function with a failure of the pilot (which will happen), then it doesn't need the pilot there in the first place.

There will be either 2 pilot airliners or pilotless airliners, but not single pilot.