I called Tauck today.
Unfortunately the weeks that I need for our Siene river cruise next year are sold out in the category we need (family of 5 requires that we have the suite, the only category that sleeps more than 2). Because of work, I can travel in June, but not July really. Also, while everything related to the land trips is transferable, river cruise deposits are not. Right now we are waitlisted for the preferred weeks, but I think we are going to go ahead and book the Alpine Adventure instead. It seems I will have a substantial credit with Air France, but I assume I should be able to get Houston/Zurich/Munich on there, KLM or Delta.
We had paid in full early for 3 of the 5. I could have received a full refund for everything I paid in, but if I left the money with Tauck, we received a $500 credit for each person paid in full and $250 for the ones not paid in full. At any time, I can change my mind and get the refund in the future.