The logic of the shift to “CE” and “BCE” demands that we reset the calendar since it’s still offensive to have to mark your dates from Jesus even if you don’t call him Lord or Christ. This will happen one of two ways.
1.) We decide to reset the calendar at some arbitrary date. Some sort of agreement gradually builds, probably under the influence of elite opinion, that we will reset our history at some set moment. We fight over some piece of legislation (or not) and it passes to set the calendar over at zero. Newspapers, history textbooks, contracts, public records, and everything else resets to confusion and inconvenience.
2.) We decide some event is so significant that it deserves to be the reference for all other times. The desire that a timeline start at some chief or significant event is the normal way of human action, though variosu exigencies force us to pick an event in human history (the date of the big bang or the congealing of the earth, even if we could get it accurate enough – which we can’t – would leave us with unmanageably large numbers.) So we’re stuck finding a person or event that we want to reckon all time from.