As you can see it’s not a zero sum game. The precautions you are implying must be taken to protect a hypothetical outlier is essentially shutting down all learning at this school, and likely many others like it.
I would suggest on balance, and particularly in light of how virulent and mild Omicron is, it’s time for the “protect grandpa” pleaders to update their mental model - what you’re saying is sacrifice everyone’s quality of life and freedom and ability to live, learn, and play, for a hypothetical outlier who has plenty of tools already to protect themselves.
Also, there are several promising therapies that should help this population. Even a few months for them to ramp up availability will help a lot.
It seems like the vast majority agree that keeping restrictions forever is too extreme, but many of the covid-conservative arguments I see imply keeping restrictions forever, because they are based on factors that are unlikely to change in the foreseeable future (like immunosuppressed people + endemic covid).
The same goes for logic that also implies we should also be masking, social distancing, closing schools, etc. for influenza (which, again, I believe the vast majority of people would reject as too extreme).
https://ourworldindata.org/grapher/switzerland-covid-19-week...