According to this piece, they are. A key indicator/quote pulled from it:
Around 30 years ago, bistros represented about half of all restaurants in Paris…Today…that figure has dropped to 14%.
Bistros are challenged because the cost of providing that type of establishment in Paris is limited by such things as rent — a problem not limited to Paris — as well as international threats like fast food joints.
At one time bistros were fast food joints. But there’s more to bistros than fast food. I agree with that article that says a good bistro should be
open continuously morning to night, serves French comfort foods at moderate prices, and houses an active bar where locals can gather for a drink and some lively conversation
That seems right to me. McDonald’s in Paris will never be a bistro, no matter how fast the food or how French they make the decor.
Paris will always have low cost places to eat (e.g. cafes), but it would be a shame if they lost their bistros. (It would also be a shame if the ones that remain are expensive museum pieces and less casual places to dine.) Best to get yourself to them now while you still can.