There are examples out there of ships designed with only one nacelle (Hermes/Saladin and Freedom spring immediately to mind), so we know a stable warp field is possible with a singular engine. These ships were always built with this in mind, but what about ships with two nacelles (i.e. pretty much the rest of the fleet), if they took heavy damage to the starboard nacelle would they be able to warp out on the port one alone? I can't think of any examples of this happening, but surely it must be an option--even for a short time.