Low fluid wouldn't affect the retraction because with most of these RV jack systems, it doesn't take fluid to retract. (UNLESS it is one of those powered extend/retract systems which tend to be rare).
It takes only a release of fluid pressure holding the cylinder rams in place, and the added pressure of the retraction springs attached to the foot of the jack. That requires only one valve, and the electrical system to operate it.
If the system reservoir was totally emptied, the jacks would still retract. But not extend.