Since there's no derailleur, the chain would do a good job of resisting that force (though since it's only on one side, maybe it wouldn't be enough, and the wheel/seat stays would twist)

Though when you start to pedal, the chain would tend to pull in and bend the seatstays, but there should be some level of force that is less than the opposite force caused by the rider's weight, so this bike could work under light pedal pressure.