score:4
It is certainly possible. The fare restrictions are simply a coded field in the ticket stating what is allowed under normal operations. In a rebooking situation (i.e. canceled flight, etc) the agents have a lot more latitude in rebooking. In the US, for example, you won't find Delta selling fares on American or United, but they certainly can and do put passengers on them in extreme situations. In other words, the fare restrictions do not impose any sort of technical limitation that would block an airline from reaccommodating you on another carrier that's not listed.
The same goes for the other fare rules as well.