Actually , not back to square one since the mRNA vaccine can be easily tweaked to be effective for a variant.
In fact so far the current mRNA vaccines we currently have work very effectively against the variants we currently have which is why the CDC said vaccinated people no longer have to mask up.
mRNA vaccines can adapt to variants faster than others: Dr Drew Weissman
Common among the two is also their platform – modified mRNA coated in a lipid nano-particle.
www.hindustantimes.com
However , if a variant of Covid 19 were antibody resistant every one us including you and the most healthy individuals would have no natural immunity or earned or vaccinated immunity to fight the virus off.
That means all bets are off and lockdowns and solitude would be the only way for mankind to survive.
To survive you would need to live in a rural area or a cave and you would need to rely on yourself to grow the food you need or you can hunt and prepare the food you need to survive.