Originally Posted by CaptainMiles

LondonElite is absolutely right. If you do nothing your EWR-RDU return will be canceled.

Here is something that may (or may not) work but which you can try. If you need to be in PHL for the funeral over the weekend and are going to drive there, check in online on Sunday for your RDU-PHL-EWR Monday flight anyway and print BPs. Print TWO copies of the PHL-EWR BPs. Then, show up for your PHL-EWR flight on Monday. When you try to board at the gate, the BP will not go through, and the gate agent will claim that you can't go because you missed your RDU-PHL flight and your itinerary was canceled. If you can say with a straight face "you gotta be kidding me, how could I be here if I missed the first flight? There has to be a mistake. Perhaps it did not scan the properly in RDU." there is a chance that the PHL gate agent will fix this for you and reinstate the entire reservation.

Why print two copies of the BPs? You will use one PHL-EWR BP to clear TSA at PHL, and use the other PHL-EWR BP to try to board. It is not wise to show the gate agent a BP scribbled by TSA in PHL, as the gate agent would then know that you entered the system in PHL.