We will go back to normal eventually, when is hard to envisage. There's several factors really.
Public tolerance, currently tolerance for lockdowns are waning, as you spoke of the Spanish flu, etc. There were lockdowns, but they were never respected to the degree coronavirus lockdowns are.
We have better social security now, furlough and grants. In those days support wasn't as great and until the money basically runs out or the market's say, NO MORE MONEY. The government will have to make a decision. At that point there will be a shift, think Brazil, they simply cannot afford to lockdown as we do. Due to poverty etc
Boomers, largely control our government, therefore they are currently serving that generations interests mainly. They are the ones generally most at risk from coronavirus. As more die their voting power decreases.
New variants emerging, truth be told, I feel we haven't made much ground. We have now created new supply chains and beefed up the vaccine industry. This helps for new variants coming along.
However as current vaccines are only 50% or so effective against the SA variant, you can be sure we haven't seen the end of this yet. We need to boosters administered over summer before winter, which seems highly unlikely. How effective are the vaccines also in the real world, we cannot be sure.