Does the compressor even turn on? Check that the air ride switch is ON or move the car back & forth a bit, you may hit the sweet spot that allows the air spring/s to hold air. If the springs refill with air, turn the air ride off to check if the bags still drop after being parked, this will confirm bad air springs if it drops again.
To lift it as it is now, you may need two jacks(oem scissor-jack & reg jack) and jackstands if you have available.
If you have coil springs up front, then that means it isn't slammed like the rear so you have some space that you can get the scissor jack underneath as close to the middle of the frame and twist it up enough to get a regular jack under the rear lift points.
Don't forget to turn off the air ride switch before jacking the Mark!
With the rear driver tire removed, check the height sensor & bracket to ensure it didn't move Up on you which would make the Mark go down. While you're down there, finagle the solenoid from the air spring to check for damage to the valve.
If curious, you can then remove the air spring and slowly flex it by hand like an accordion while paying attention to the bottom of the rubber diaphragm that oscillates. You'll probably see a nice clean section of rubber with some rock pits before coming across some cracks that'll appear where the diaphragm folds over.
Hopefully those rear springs will come in sooner than later.
