If you have position feedback / limit switches, program the lift such that if the limit switch on top is hit (when the lift is at maximum height), it can only go down or stop.
The second way is to go into one of the default files (some other team did it and posted the code on here before - I will try and find it) which adds a logic that says if data isn't refresh in a certain amount of time, it sets all the joystick inputs to zero / default.
EDIT:
here is the link with said thread.