This is all a bit academic now; if the OP was able to change her ticket so that it had an overnight stop, she would also have been able to change her ticket so that it had a stop of more than just one night (if she deemed just one night as being insufficient). As reported, the cruise line was not interested in looking at changing the flights at this vast remove.

However, if/when changing the ticket became a viable option, she would have changed the ticket in a manner that would not have needed her to "drop" the final flight, and therefore the issue of baggage disappears (one should always carry in one's carryon what is needed for at least one overnight stay, on the assumption that your luggage may be delayed).

The KLM website previously stated that overnight stays at AMS allowed checked luggage to be short-checked to AMS; it no longer clearly states that (though reading between the lines, if you force your stopover to be greater than 24 hours, you should be good).

But be in no doubt that KLM will seek a fee for short-checking a bag where they decide that you have no automatic right to having your bag delivered at AMS.