My understanding is that herd immunity without vaccine requires approx 600 000 deaths in this country (unless the science has changed since last week), is that really what you are suggesting?
Not seen that particular model but there is no 'requirement' for a number of deaths - there's an estimate of how many it might involve in the models - based on what I've seen that would be at the very extreme end but they are changing all the time. The problem is even with herd immunity the vulnerability of individuals doesn't change - so until there's a vaccine the vulnerable would need to be shielded, or take more risk on the basis if we've reached herd immunity there are many fewer infected people out there spreading it. This all depends of course on whether you can catch/spread it again once you've had it once - if you can, we're knackered until there's a cure or a vaccine.