Under the new EU reg, they would have to re-route you to your destination 'under comparable transport conditions at the earliest opportunity'.
What is likely to happen is that they would offer you a re-route at the earliest opportunity on one of their flights (i.e. refuse to re-route you on an alternative carrier), even if the only available flight of theirs is 1, 2, 3 or more days from the original date.
It is a grey area in the regulation whether a carrier would have an obligation to reroute you on an alternative carrier if they cannot offer you a reasonable option on one of their flights, and you can bet that FR will defend an interpretation of the regulation that minimises their obligations.
In any event, they would have an obligation to put you up in a hotel and cover meal expenses. As others have said, you would have to be prepared to fight for this, as FR will drag their feet as much as possible to comply with their obligations.