Permanent restrictions, drastic social change, and large contact tracing infrastructure might keep it under the herd immunity threshold of ~60%. It might not, too.

But you can't let up at any point, because it'll still be endemic and ready to explode up to that herd immunity threshold.

I prefer approaches that get us to that 60% in an orderly fashion-- staying short of healthcare overload, and preventing as much infection in the vulnerable as possible.