Suicide Pact

In Heather's letter she talks about how her and JWJ are not of this world and and can't wait for them to get on their boat and sail away. She then mentions them crossing the Styx. The Styx is the river between this world and the underworld in Greek mythology. It holds the tortured souls of those that can't afford to pay the ferry to cross. Is she planning a suicide pact for her and JWJ? Or is this just a metaphorical analogy? Did JWJ intend for this to be a suicide pact or was he luring her in for the kill?