A couple had a less-than-desirable Rhine cruise aboard a Viking river ship that broke down short of their final destination. The balance of the trip was done by bus and hotel, and they are suing Viking. See the story in the New York Daily News. I don't expect them to win the suit.
This reminds me of something I need to share with you about river cruising. If the river is too high, the ships cannot squeeze under the bridges. If the river is too low, there isn't enough water under the keel to navigate. When either happens the firm doesn't tell you to stay home; they tie up the ship and take you on a bus and hotel tour.
Needless to say this leaves people who wanted a river cruise very bummed. Instead of unpacking once and having your shipboard "hotel" room follow you around Europe, you live out of suitcases and sleep in a different bed every night.
Face it, if you'd wanted a bus tour you'd have booked a bus tour - there are plenty of them offered. We've river cruised many times and only been "bitten" twice when, both times, low water caused the first day to be done by bus. Fortunately they didn't have to cancel the whole week or more on the river.
In spite of this risk, river cruising is a real favorite of the DrsC. The empty ocean is boring to look at; a river bank is almost never boring. Navigable rivers tend to have lots of barge and ship traffic to watch and it passes right by your ship.