I’m pretty sure this doesn’t have a straight factual answer, so in GD it goes.
It is currently the year 2009 Anno_Domini. Suppose that Christianity never caught on, and ended up like Mithraism and other cults. Dionysius Exiguus never did his thing, no BC/AD, no Gregorian calender, etc. What year would it be?
Would we have stayed on the Julian calender? Would it currently be the 1st year of the reign of Obama I? Would someone else have come along to reform the calender, without D.E.'s reasons? Would they have made another fairly arbitrarily old system/new system starting point? Were there any other serious contenders for the calender system at the time, or since, that might have been used?