Bought wife's prius with a bad cell in its hybrid battery. Tons of warning lights came on in the dash, including a big red triangle.
While the battery was bad, it still had enough oomph to start the gas engine, which ran all the time, and didn't shut down at stops. Car was much slower to get up to speed. Had no ABS, traction control, or air conditioning.
The car's diagnostics were very very good and could pin down which cell (technically a "module") was kaput. I disassembled the battery and replaced the module with a good condition used one from ebay. The battery control computer has wire probes that lead to each individual cell so it knows how things are going in there.
Car's had 25k since then and still gets 50 MPG in the summer.
How your Fusion will behave depends on its engineering, of course. My "other" prius, a shade junkier, ate one coil pack out of 4 and then shut down the gas engine vs running with it misfiring. I had 1/2 mile on the electric motor before it coasted to a stop, inconsolable.