I think it's reasonable to have a culture where you're encouraged to consult the IC who wrote the code even after they've moved on to other projects. But I don't think they should be responsible for fixing the bugs.

And I don't mean this to excuse the bad code written by ICs. I just think it's not sustainable from the POV of the org itself to depend so heavily on individuals, especially ones who aren't familiar with the entire codebase anymore.

The team currently in charge needs to have full ownership and be responsible for the code, even if they didn't write it.

That works as long as there's a finish line. If you make a framework, or a set of libraries, it's easy to get pigeon holed into all new features/tangential work around those.