I think it's more than safe to say that something needs to be done about EWR if CO wants to continue international growth. Airspace already is jam-packed on the east coast corridor. The runway configuration only allows one takeoff and landing at a time (instead of two at a time, like larger aiports with parallel runways) and in bad weather, often only one runway is open for both arrivals and departures. In addition, EWR is packed with RJs. If a flight experiences a mechanical as in the OP's case, it can take ages for a landing slot to open. And let's not forget about the numerous ground stops for flights inbound to EWR.

CO needs to relieve some of the pressure on EWR so that the airport will develop a better reputation. If EWR continues to nuture its poor reputation, a danger exists that pax will book away from CO for their international travel in order to avoid the airport. At present, I have colleagues who are of this mindset - they were burned one too many times at EWR and now use other carriers and other airports for their international travel.

In the short term, CO should use the ExpressJet loss to reduce the number of RJs operating into EWR by at least 10% and select a European route that draws sufficient west coast, midwest, and southern o/d traffic to justify creating a CLE nonstop (like AMS or CDG). In the long term, I'm not certain that CO can do much else - EWR seems to be operating at maximum capacity.