As someone calculated earlier, front seat crew account for about 2% of the price of a ticket.
Probably even less for long-haul operations (with more pax aboard).
All the sensors and computers required, in addition to the advanced AI required to make the airplane autonomous, will surely cost more than pilots for a very long time.
And by the time it's not the case anymore, it's possible that there won't be enough petrol to continue flying airplanes.
So there's a serious chance we'll never see autonomous airplanes in our life.