My organization has perhaps the largest number of FSA participants in the country. Confirming Julia's observation, we set up our LOA practice based on how we wanted to handle it, not based on any survey data which may or may not have existed.
(At this point, please excuse the change in terminology to Leave Without Pay or LWOP in our vernacular. Employees on Sick or Annual Leave continue participating in FSAs just like active employees unless there is a "qualified life status change.")
We require employees on LWOP to continue participating in the FSA program for up to 8 consecutive full biweekly pay periods (16 weeks), or the end of the FSA plan year, whichever comes first. During that period employees are required to continue their contributions and they still have access to their FSA funds. If the contributions are not paid by the employee during the LWOP period, it is recovered when they return to full-time status.
Participation in the FSA ends after 8 biweekly pay periods of LWOP. No more employee contributions; and claims after that date are ineligible for reimbursement.
There are more arms and legs to this policy, but that's the gist of it. If you want to learn more about our policy send me a message by clicking on the envelope under my picture and I'll send you our administrator's email address.