Aegean would never state that, but it's a given for all "new" and/or "seasonal" destinations we have seen the last few years. Take for example all these new routes that announced for next summer. I am pretty sure that not all of them will make it in the end.

For your question: If A3 cancels the EIN service (we hope not, since it's conveniently in the afternoon), switching you to AMS would be very easy and i think it's the policy they follow. For example, last summer when they cancelled the PMO service (way ahead of its begin), they offered me either full refund or rebooking to another airport in Italy. I went for CTA.