I'm in a similar situation. If I leave and don't get back on the still-not-cancelled flight Sunday morning (12:30am) I won't make my next flight on a different itinerary, scheduled for 4+ hours after my return to PHL. There's close to zero availability returning to PHL/EWR at all, never mind in a specific (inexpensive) fare class. I've chosen to purchase a relatively inexpensive refundable one-way ticket back to EWR for Sunday night so I at least have a reservation on *some* flight in case my scheduled one is cancelled. If I need to take that flight I'll be left with a car at PHL, needing to be in BOS, and with tickets from PHL-MHT. What a mess!