Who gets to draw that line?
Me. I get to draw the line. It's all on me. Didn't anyone tell you?
Errr, maybe someone else......
While I fully expect different levels of government to all have a yardstick, since it's 100% definitely a policy question, there's going to be a natural line too. If policy set's the level significantly higher with more illness allowed, economic impacts will not recover. People will avoid stuff on their own. If policy set's the level significantly lower, people will ignore recommendations. In that middle band, there's lots of room for different policy disagreements.
If I was setting the policy goal, somewhere around 100 deaths a day sounds plausible. That's 100 * 365 = 36,500 a year. I'm sure some will argue it should be lower, and others would be fine with 200, 200 * 365 = 73,000 a year. Both the flu and motor vehicle fatalities are near those ranges, closer to 100 than 200. And many have repeatedly pointed out that we don't take the same disruptive mitigation efforts for those.
Maybe we'll come up with less disruptive mitigations too. The vaccine is the probably the least disruptive, few sore days and mostly happy. But, whatever we do to get infection impacts down, my guess is that most mitigations being removed will require that we get daily death's under at least 200 and are able to keep them there without the mitigation that's being removed.
From covid19.healthdata.org we're currently over 3,000 per day. That feels like a long way to under 200 still.