well, the EX-Gear IS the seat (it's like a valk, but rather than a robot that turns into a jet, it's a robot that turns into a chair),
and I think they just leave the EX-Gear in the plane unless the pilot ejects with it.
edit: as for the G compansation thing,
to quote the compendium (from the VF-15 entry):
the pilots survive high G's through systems that temporarily make the body more resilient to G loads up to a point. beyond that you still die.
I think in some way's it works like energy conversion armor, except on your flesh and bones.