If you mean installing a Rolls engine, it may not even be practical - on most aircraft the interfaces are totally different (I don't have any knowledge of the A380 - there was an attempt at 'plug and play' on the 787 but last I heard it hadn't been certified). Then getting an experimental ferry permit would be a nightmare.
I find it hard to believe that there are not spare GP7000 engines available - the very last thing an engine manufacture wants to do is ground airplanes because there are not sufficient spares. It tends to make the customers look elsewhere next time they are looking to buy. If the EA were planning to cease production, they'd make darn sure adequate spares were available first.