Hi Gnopps, I believe that NickB is right. The return flight on KL is cancelled. They offer to reroute the pax at the earliest possibility, which is the next day. If KL had another flight the same day, the earliest opportunity would be that KL flight IF there were seats available.. AF is legally a different airline and I don't see any legal reason why they have to reroute you on AF same day.
Of course, according to 261/2004. you always have the option to request refund.
The third option you mention is at the convenience of the pax. So if he/she prefers to return three days later and there are seats available, the airline is obliged to do it at no cost to the pax. But there is no mention of accomodation costs and no reason for it as it is at the pax convenience.
I understand very well ctkaty's frustration, but they were advised some three months ahead of the cancellation or change of schedule, so easy to get refund and make other plans (at least that would be FB claim).
As other posters mention, while there are no legal avenues, pushing FB hard for a "commercial gesture" to free some award seats on the AF flight might work. But note that this is not a trivial action for FB/AF/KL and that it would greatly help if the pax hold status with FB.