I would try getting new push pins first. Easy enough to try, and if it doesn't work, you can go to plan B.
I had an issue under warranty once where they replaced the back because the clips were broken.
It came off again after a few days, and I had to put it back on myself. Just make sure the push pins are engaging well into the holes in the tabs on the bottom of the seat.
2008 Space Gray Z4 3.0 si, Saddle Leather interior
2011 Nissan Frontier King Cab
2010 Lexus RX350