If there are no buyers then they are worthless!
A friend who is in the jet trading buisness told me that B744 with GE engines are still selling for conversions but at lower prices and much slower rate than 2 years ago, but a B744 with RR engines are not really marketable for conversion as world wide support is not good compared to GE or Pratt, and the RR machines are heavy compared to a GE machine.
He could be correct about that as in a former life I remember QF, NZ, BA and CX had to have an engine pool agreement for a spare engine sitting in LAX.
The QF GE powered B767-300 will probably sell well, though would being the lightweight version reduce the conversion potential?