No one (from Regent) will complain about black sneakers - most of the people on board probably have issues with their feet and cannot wear other shoes. It is very common.
For purposes of Covid "coverage" by Regent (or by your insurance), you need to establish that you do NOT have Covid prior to starting your trip. Starting your trip is the day you fly, the day you stay in a hotel (if driving) or the day you get on the ship (if you drive directly there).
My advice is simple. If you are worried about getting Covid, stay home...because once you leave your controlled environment, it becomes a distinct possibility. Relying on others to keep you from getting sick is a Fool's Errand.
You can get your flights for the return as well no matter what the return - I've seen/done it. The reason is that Regent holds the flights from their allocations and doesn't ticket them until later.
I would escalate that to his supervisor...they have lost their jobs for far less. The supervisor will review the call...they are recorded...and solve the situation.
Better for Regent to buy the ticket and not the passenger, yes?
And yes, the Reps will put you directly through to the Air Desk in the event of an emergency.
This isn't a Regent issue, this is an airline issue...and while you can interface with the ticket counter directly, can you transfer your booking to the next port on the cruise without buying a new ticket?
In an emergency, you can call the Air Desk directly...I have done so. However, if you miss a flight, Regent will fly you to the ship. If you need to change your flight destination and you booked it yourself, you are buying a new ticket right?
No doubt it is far easier to book your own...but losing the support of Regent in the event of a problem with your flight...not sure what can make up for that.