It's worth doing the shocks and springs as the ride will be choppy with the standard shockss and they will wear out quicker as they are not designed for lower ride height.
Springs can dislodge with standard shocks, but it is very rare and normally would only occur with lowering springs of minus 60mm or more on standard shocks. More likely it is to be a problem at MOT if the car is jacked in the air and on some cars (V**xhall rear suspension) the springs can fall out, which some MOT places fail the car on.
Cheers
Biz