My real world DC Universe... would end in 1960 and we'd just get new stories set between 1938 and 1960.
And then another real world DC on another Earth that goes from 1960 to 1980. And then new stories set between 1960 and 1980.
And then another real world DC on another Earth that goes from 1980 to 2000. And then new stories set between 1980 and 2000.
And then another real world DC on another Earth that goes from 2000 to 2020.