[nradov]

There is no "evolve into a cold" hypothesis. SARS-CoV-2 already is a cold for the vast majority of youths that get infected, just like the other four endemic common cold coronaviruses. The only reason those other viruses don't kill as many people today is that most of us get infected as youths and then the resulting natural immunity gives us some protection later in life.

Symptomatic reinfection is possible but remains rare. The Delta variant is more contagious but there's no reliable evidence that it has a higher fatality rate. Vaccination cuts the fatality rate close to zero.