1.) e certain fee is 15 EUR per transaction for the rebookable fare ("Normaltarif") from the day of validity.
2.) Not rebookable fares (Sparpreis 25/50) can't be returned. They can only used with the trains booked in advance and against a fee with any other train on the day of validity. But this fee is 15 EUR PER PERSON PLUS the one-way difference between Sparpreis 25/50 and Normalpreis.

But I think it really doesn't make sense to get a bahn.comfort-card when not travelling by train. When travelling the service in the lounges is exactly the same for the 1st class IC / ICE traveller and the bahn.comfort-customer (with the only exception that the bahn.comfort customer can bring in one guest even when the guest is not travelling.)
Very good coffee and hot chocolate, soft drinks free of charge and a most times quiet environment (except Frankfurt in the afternoon hours ).

And the other bahn.comfort privileges are more or less marketing issues except the 5% rebate on the hourly/daily/weekly rates of the DB Carsharing. The reservation privilege (reserved bahn.comfort seats) is a privilege o getting a seat reservation and NOT GETTING a CHEAPER FARE on sold out trains. (Whatever sense ist makes to make train reservation as complex as flight reservations).
As DB AG has lost many customers on the latest price changes there`s much space in nearly every train in 1st class except friday afternoon and times with extraordinary demand. In 2nd class many trains are even empty except some times when they launch a special offer.