Question: why do abigail and mercy run away?
Answer: In Act 4 it's revealed that Abigail has run away and stolen money from her uncle (and so her reputation takes a hit in her absence), but since she is no longer in Salem, it doesn't really matter for her. ... In Act 2, Abigail still seems to want to be with John Proctor, since she's accused Elizabeth Proctor of witchcraft.