From my multiple demo experiences last year (probably about a total of 15 sets on slingshot boards) I never had the liners pop out... but then again i don't think i ever crashed hard enough to completely come out anyway.
I am nearly positive that the liners will ALWAYS stay with the boot. There is more resistance/ friction on the liner against the shell in coming out than your foot against the liner.
Also, if you are worried about having to pull the liners out with your foot when removing the board... DONT BE. I know alot of guys who complained about this for '07. The reason being, THOSE guys didn't loosen the laces completely. Loosen all the laces completely till the tongue opens up like a trap door (the same as when you first screw the bindings to the board)hold onto the liner and the shell then take out your foot. It should be nearly as easy as removing your night-time slippers.
Also, the easiest way to put the liners back in is to invert your hand (palm up) then insert your hand inside the liner like a foot till your fingers touch the end of the toe box. Then insert the liner into the boot, curving your hand in a cupping manner to bend the foot portion of the liner into the foot area of the binding shell. hopefully that makes sense