Past large scale shows were maybe 2% live: the live parts being drums, percussion and bass. Everything else was playback (or in some cases, played at such low volume under pre-recorded tracks that no one could hear). Keep in mind I'm a musician myself and I can tell the difference in sound and performance when an artist actually plays a piece live.
Monaco had plenty of little live bits and pieces over pre-recorded material, but in terms of JMJ's performance: he didn't play any lead melodies live (Oxygene 4, Chrono 1, 2 & 4, Rendez-Vous 4, Vintage, etc). What he actually plays live are the following:
Keytar solo's
Laser Harp
Therimin
Sound/Sample pads
Little incidental pieces
Variation 3 improvs
For example the main lead melody for Chronologie 4 was not played live by Jarre, but the synth solo at the end (on the Nord Lead) was live.
His "partners in crime" are a bit harder to pin down (because the camera isn't always on them); but for Monaco:
-The guy who replaced Dominique is mostly doing the "side solos" that embellish/compliment the main theme (RDV 4, MF 2, for example) and he was adding some live sequences to other tracks. I believe he does some pads and bass as well.
-Francis does pads, bass and some lead melody playing (to which JMJ is miming). Sometimes he seems to "fake" sequences; but he's the real keyboard virtuoso in the band. Past shows like China and Gdansk basically had him mime the whole performance, which is a huge waste of talent in my opinion.
-Claude does the percussion and seemingly not much else. You'll notice he's surrounded by synths but those are only for show. Variation 3 is probably the only song in which he adds synth playing of value. During the In Door tour he was in change of staring and stopping the payback of every song (from what I remember).
La Defense was all playback synth wise. But the drum, percussion and bass players were excellent and I would love to see him work with those guys again. Musically it was one of his best shows; the arrangements were superb and full of life (even if not performed entirely live).
Here's what Jarre played live at La Defense:
-Camera click sound during Souvenir Of China (he presses a little button on the side of the keyboard)
-Laser Harp during Calypso 2 (you can hear his playing on the audience/radio broadcasts)
That's it. Everything else was for show.
The other synth players weren't playing anything that we (audience/TV viewers) can hear. (With the exception of Dominique's keytar solo at the end of MF2, which I believe was live. And he looked terrified.)
It's all part of the show; the overall experience. Jarre is giving the audience an "impression" or "illusion" of live performance without any of the risk. His band was simply another facet of the spectacle; not meant to be the main focus.
On the current 2011 tour you'll still find him mimming the lead synth parts, but hes paying the more improvised parts live (keytar solos, laster harp etc)-- hes more comfortable with this.
Other shows:
China 1981: He plays some parts live
Houston/Lyon: JMJ mimes the entire show
Doclands: JMJ mimes
La Defense: Mimes
EIC: Plays some parts live; mostly playback (on his part)
CPLT: Plays some parts live; mostly playback (on his part)
Oxy Tour 97: Plays some parts live; mostly playback (on his part)
Moscow: Plays some parts live; mostly playback (on his part)
Egypt: Playback
Greece: Plays some parts live; mostly playback (on his part)
Denmark: Plays some parts live; mostly playback (on his part)
China: All playback
Poland: Mostly playback
Oxygene Tour: PLAYS HIS PERFORMANCE LIVE
In-Doors/2011 Tour: Mix of live playing and playback (for JMJ).
End.