Just to add a few points here....
Tadjr is correct. It would be a no win situation. If you leave everyone standing in a line at the airport for hours to get rebooked, you were wrong. If you offer alternative measures for rebooking, you are wrong because you are passing the buck and trying to get people out of your face.
My opinion - the supervisor that met the flight could have done a better job of communication customer OPTIONS. 1) Remain here in the airport and we will do our best to rebook you as quickly as possible - while explaining that there were no flight departure options available for this evening. 2) Offer the reservations phone number as an alternative to staying at the airport - calling the reservations number will provide you with the same options as staying at the airport. It is all about how you present the OPTIONS.
What it sounds like is the supervisor more or less just handed out phone cards and told people to go.
My experience - Some people will do what ever it takes to get angry customers out of their face so they don't have to deal with it. I deal with stations on a daily basis that "hub dump" and seek assistance in doing what should be done from the get go, such as rebooking misconnects. RES becomes a convenient dumping ground. my experience is also that when customers are given the option of using RES to rebook, they will remain in line, on their cell phone. They will rebook with reservations and then get to an agent and continue to press and make sure that there are no alternatives. (Because they don't believe the voice on the phone, but believe the person standing in front of them)
There is no way that we are ever going to "win" in this situation. Make people stand at the ATO at midnight trying to rebook 270 people - we would be torturing them. Send them to the hotel to rebook, and we are absolutely no help and offered no assistance.
Looking at the operational planning part of it, I have seen many times where we have had similar incidents of A330's turning back and you are hard pressed to get reserve Pilot Crews since most do not live in PHL and commute home after the last transatlantic departure. When reserves are called, since they are not in base, they sick the quick call. (Not saying this happened here, but I have seen it more then a few times.) If this was a planned "quick" fix and the crew was still legal, then they were doing what they could to try and get the flight back in the air. "Hysterical" customers in the jetway that want off, compound the problem due to Positive Bag Matching. Where we may have been all buttoned up and ready to go, 1 person gets off the plane and you have to dump the plane to remove bags, and now you are out of time.
Regarding the "spare" A330 and running a 767 - I am quite sure that th first thing that they looked at is using the RON A330 in PHL. Depending on what the MX package was on the A/C would determine if the aircraft was usable. Also, since those airplanes get in early in the afternoon, there may have been MX items already in work. Once you start the work you are pretty committed to finishing it. Using the 767 to FCO would not be a possiblity. You would have no crew to bring the aricraft back - until this crew had their legal rest. Are 767's permitted to fly to FCO in our Ops Specs? I am thinking no. If FCO were in the ops specs for the 767, how many people would you be able to carry to make it? How do you decide which of the 270 customers get on a 200 seat airplane - and that is before the weight restriction.
Things are not always as they seem on the surface. You can call into question everything that happened, but unless you were actually there, with all the facts, you have no way of knowing for sure what all the factors were that drove the final out come.