The 2030 target is merely an "aspiration" and 100% WILL be pushed back.
It's basically a "nudge" to get "those who can" to move over to electric, i.e. those who it works for, those who have drives to charge on, those who can afford to pay more, those for whom journeys can be planned around charging.
It'll be a success if it can get half of the cars running on electric.
Cars last an average of 13 years at the moment and it's not particularly rare to see cars much older, typically 20 years, so even if sales of new cars were banned in 2030, there'd still be petrol cars on the roads until well into the 2040s so we'd still have petrol filling stations etc.
But anyway, not all countries are banning petrol cars, so there'll still be new petrol cars being manufactured - maybe not the main brands who seem to be phasing them out, but they'll still be out there. That means people can buy abroad and import, and of course, immigrants can bring them in with them as they do now, so they'll still be available for people to buy on the second hand market.
Of course, "hybrids" are being allowed until 2035 I think, so that'll be another deadline to be pushed back. In fact hybrids may be the politically acceptable answer, i.e. cars mainly running on petrol, partly assisted by a small battery, to "tick boxes" of reducing emissions, but in reality, not by much.
At the end of the day, getting as many people as possible to switch to electric will help the environment and tick boxes for the politicians. It doesn't need to be everybody, and in reality, will never be everybody. I'd say if they reach 50% of cars on the road being electric or hybrid, it will all have been a success. Trying to hit 100% is never going to happen as the infrastructure will never be there, especially in more rural areas, and the costs will be way out of proportion to justify it. It's ALL about picking the easy fruit - those who can need to be "nudged" to do it, those who can't will just continue with petrol cars for another 2 or 3 decades at least - that gives them time to adjust their lifestyles, careers, etc.,