As seen from one of the links above, the glide angle of many a/c is quite respectable. It quotes a sub-sonic jet transport at
16-18:1. I believe the 747 that flamed-out all 4 when it flew through a volcano plume managed 20:1 during a part of the 'drift down' to re-light height of 10,000' and managed about 120 miles.
The Gimli Glider in the other link proves how efficient big jets are as gliders.
Our PA28 manages over 10:1 with a windmilling prop, I hope I never find out what it's like without a prop at all!!!!
It's a common mis-conception that powered a/c fall out of the sky when you take away the power.
Sadly, the Mossie does appear to have big asymetric power problems and I can well imagine you'd be better off reducing power on the good one. It would make an enormous difference of you could get the prop feathered on the dead side, but I can't see any reason why it shouldn't glide. After all, even the Space Shuttle is a glider (angle of 4:1).
Cheers,
TheOddOne