To answer my own curiosity, I did a little research today in my spare time and I found info at the following page :
International routes are also covered by the Act but it does not apply to foreign carriers. For example, passengers holding tickets on a flight originating in Kansas City connecting to London on a U.S. carrier could only be accommodated on another U.S. carrier flying between both Kansas City and London. If the passenger was to fly beyond London to a point not served by another U.S. carrier, the passenger would most likely be accommodated to London, but not necessarily beyond. It follows that if there is only one U.S. carrier flying to the international point and it ceases operations, foreign carriers are not obligated to honor the ticket. If the insolvent U.S. carrier is in alliance, it should be assumed the other alliance members will honor the ticket in some manner.
If the insolvent carrier is the only one operating between a city-pair, there does
not appear to be any obligation for other carriers to honor the insolvent carrier's
tickets since there is little likelihood they will be compensated for carrying the
passenger....