The rule of thumb I hear is that, in a mature product, reading and maintaining code takes about 10 times as much effort as writing it in the first place. I've never tried to measure this myself, but it doesn't seem to be wildly off from what I see at work, so let's go with it. Let's also assume, for the sake of argument, that these AI tools double the productivity of people writing new code. Or, equivalently, they halve the time it takes to write it. (This is a lot more than what I see people typically claim, but I'm trying to steelman and also it makes the math easier.)
Anyway, this would imply that, speaking purely in terms of raw productivity (not, say, security or correctness) the AI coding assistant is a net win when the code that's written using it is less than 5% more difficult to maintain.
And I'm inclined to think that, if Copilot & friends are enabling more people to write more code that looks like what we see in this article (also not wildly off from what I see at work), then it's hard to see how they could possibly be making codebases where they are used less than 5% more expensive to maintain.