For 2, it’s unlikely to mutate to the point of not being recognized within a relevant timeframe. We can track how fast it’s mutating reliably, and it’s not dangerously quick. The good news is if we have immunity, it should last for several years if considering only what we can see about the mutations. Follow the NextStrain project and Trevor Bedford on Twitter for a smarter analysis than I can provide here.
We have studied corona viruses before so we have information about mutations and immunity. We have also been watching covid-19 for these for 4 months.
So this is 100% untrue - "Currently we don't have any evidence that either assumption is true"
"for very little benefit." - We are talking millions of millions of lives, so I'm not sure why you'd say this. The lockdowns are killing millions, a lot of them are the very poor.
We need to plan for the fact it might mutate or we are not seeing immunity stick. But that's different to throwing out Giesecke approach because we don't know something with certainty.
So soft lockdown in maybe a year or more, deaths will be in the 0,5% vicinity, more in some countries, less in some. Hard lockdown in the same timespan as above. Less deaths but will you have any society to return to? If you do hard lockdown for a while and then lighten up you're in situation 1 basically or forced to lock down soon again. Number three is very attractive. Had we all been prepared and had plans for this like South Korea and being island nations with easily shut borders like NZ it would have been simpler. But most countries were not and are not any of that.
I don't know who came up with the idea that the goal would be heard immunity. Arguably, a "lockdown until vaccine" strategy is more clearly focused on (artificially) reaching herd immunity.
This particular error on my part I regarding the reasons for the lockdown I attribute to Tomas Pueyo and his hammer-and-dance amateur epidemiology blog.
Every person who merely delays getting COVID-19 until better treatment is available is a win. Even if it succeeds by other metrics, the Swedish approach will fail (has already failed) by this one.