RMC, yotty is absolutely correct - what you are referring to is a loss of oil quantity indication. Oil Quantity Indication is not the most robust signal in the world (sometimes the float sinks), so typical QRH instructions are to monitor oil pressure and oil temperature and operate the engine normally as long as pressure and temperature remain within normal limits. IF oil pressure and/or temperature are outside normal ranges, immediate shutdown.
Basically, if the oil quantity is really zero, the pressure will rapidly decrease and the temperature rapidly increase outside normal limits within a minute or two - and if you don't shut down the engine a serious, perhaps catastrophic, engine failure is guaranteed.
In short, operating any turbine without oil is a recipe for disaster - there have been several uncontained failures of Rolls engines when lubrication problems resulted in bearing/shaft failures.