The last we hear of Abigail in the text is that she, along with her friend, Mercy Lewis, robbed the Reverend Parris, her uncle, of his life's savings -- thirty one pounds -- and run off to board a ship (as Parris reports to Danforth). Betty Parris heard her cousin and friend discussing ships the week prior, and after Abigail had been missing for a day or two, Parris put two and two together and checked his strongbox. The play gives us no additional clues about where Abigail has gone or what she might be up to.
My text also has an epilogue of sorts, called "Echoes Down the Corridor," which references the Boston prostitute story that others have mentioned. However, history has left no real substantive clues about whatever became of the real Abigail Williams after the trials were over. The real Abigail was eleven years old, not seventeen as she is in the text, and there was no relationship between herself and John Proctor (who was around sixty years old in real life).