As a seasonal employee, and mind you a bunch of "originals" quit or were fired at my center, I was told I'd be kept on without interruption. As the man said .. "Damn, it feels good to be a gangster"; until I'm not, obviously.
Seasonal as in a driver or PT preload or local sort shift.
If you are talk a seasonal driver you chance of getting called back are slim to none. They are probably going to be laying off a couple of the junior drivers becasue of volume droping and there is a 6 to1 hire ratio of inside to outside hires. Then if no one is retiring there isn't going to be an opening. They could call you back again as a seasonal driver in the summer to help cover vacations.
If you talking PTimer they most likely not lay you off and just keep you working.
In either case if they do call you back before March 2 your senority date goes back to the first day you started working. IF they call you back on or after March 2 you have to complete your probation period all over again.