Board Thread:General Discussion/@comment-30388913-20170215175848/@comment-33470269-20171018193538

Well, after you enter True Lab, you can't abort Pacfist Run, and after you kill Sans, you can't abort Genocide Run, except if you reset. ( Deleting the files or a simple in-game reset. )

Probably if you go back, the "But nobody came" will pop up anyway.