For information purposes re Regent flight deviations, this was our experience for flights from NYC area to Athens and a return from Rome on an October voyage. Our first choices, given to our TA, was for non stop flights to and from JFK. Regent offered us a flight from JFK to Athens, non stop, on Delta/Virgin with a charge for the deviation and an additional $3,000 pp. Alternatively, Regent offered a United non stop from EWR with no charge beyond the deviation fee. We accepted. On the return from FCO we asked for the Delta non stop to JFK We did not want to return to EWR. We were offered the Delta flight for an up charge of the deviation fee and $1300 pp. We accepted this. This process was completed in 2 days.
Regent Air told our TA we could avoid the deviation fee and any upcharge by accepting either an Air Canada flight coming or going with a change in Montreal (very short layover). Or, a Swiss Air flights with a change in Zurich (also a very short layover).
We priced out the flights we have arranged to learn the cost if we booked the same on our own. The price came out to $6,500+ pp. In the end we go to and from in Business class non stop flights for approx. $1500 pp.