Mechanical and software failures will always be possible. However, we already accept a really high rate of death and injury when both could be eliminated. I don't think that will change with self-driving cars.
Adding a camera is cheaper when it results in being able to eliminate hundreds of pounds of metal and airbags. We don't make bus riders wear a seatbelt because it just doesn't solve a huge problem. When the injury rate of car passengers gets to a similar level, we probably don't need seatbelts there either.
Cars last for ~25 years in normal use (average car in US is 11.5 years old and accidents take many out before reaching their lifespan). So, at a minimum we are talking 50 years before essentially every car is even capable of being self driven. Laws are unlikely to change before self driving goes from a novelty to assumed behavior call it another 25 years at a minimum. Now, add a few more years for phasing in the law, and then a few more for statistics to validate reducing safty equipment.
So, 100+ seems fairly optimistic as that's the happy path assuming zero major issues show up.
PS: Adding a camera may get cheaper over time, that does not mean it's ever cheaper than not having one in the first place.