Each gas generator is coupled via fluid (exhaust gas) to a power turbine which is directly coupled via a clutch to a reduction gearbox and onward via a shaft to a thrust bearing and finally a large water jet.
The "directly coupled via a clutch to a reduction gearbox" is my concern. Clutches can fail, as can shafts and reduction gearboxes. Be sure that the control system can tolerate these without permitting a destructive power turbine overspeed. Put these questions directly to the GE people, including any results of their loss-of-load tests.
Further, if both engines are driving a common gearbox, what happens if one engine is running, the other is shut down, and its clutch is dragging? Will the power turbine bearings in the shutdown engine be running dry while the shaft windmills?
GE has plenty of experience going back 4 or 5 decades with these issues, so they should have ready answers.