When an engine separation occurs, because it is a physical breaking of various lines and wires etc. you can expect to get many warnings, some, like a fire warning, are likely to be spurious as there is no engine and therefore probably no fire.
As there is no engine to consume fuel, fuel consumption will go down if the fuel wing valve is still able to be closed. Just how and when an imbalance may occur on a 747 will depend on your fuel configuration, are you running off the centre wing tank or the wing tanks? The captain and his crew will evaluate the situation and set up the fuel panel accordingly.
Bear in mind that after an engine fire, severe damage or separation you will only be looking for somewhere to land as soon as possible, so, providing fuel is not venting uncontrolled to atmosphere, it is highly unlikely that a serious imbalance will have time to develop before you are back on the ground.
Sorry if this sounds a bit simplistic CAP56 but from your posts I have assumed that you are not a pilot, particularly when you make a statement to the effect that; "I have made up my mind on this one many years ago"!
There are so many variables that you can never, safely, "Make up your Mind" If you told us where you are in aviation it would make answering you a little easier, perhaps!
