Not looking for a PC Friday question as a simple yes or no will do.
Is the story of Purim believed to be real?
The answer you are looking for is yes.
The subtext you weren't looking for is that certain aspects of the story may have happened in a few different ways. There's lots of commentary on finer details, including conflicting accounts. However, the main blow-by-blow detail as recorded in Esther is believed to have happened.