irishguy28

You should first check if Aegean will rebook you onto this other carrier (without knowing the route/carriers in question, we cannot indicate how likely this is to happen, but depending on the airline(s) that would be required to accomplish this, it could rate anywhere from likely to impossible).

You should also check how much it would cost you to buy a new return ticket; this is likely to work out far cheaper than turning your existing ticket into a one-way, and buying another one-way separately.

Only once you have ruled out these options would I proceed in the manner you suggest.