You really have three problems here. The first is whether the person has gone back to work for the same "employer." You might want to check out the "
Fields letter" on trying to distinguish whether you have one employer or multiple employers when you have various governmental entities contributing to the same plan. Basically, the rule at this point seems to be pretty much that you can take almost any approach you want, but you have to take it consistently.
See, e.g., PLR 200028042 (April 19, 2000.) Thus, if the plan is treating the all contributing employers as a single employer for other purposes, it probably needs to do so for this purpose, too.
If the person has gone back to work for an entity that is treated as part of the same employer, some old guidance suggests that the person would not be treated as having truly separated from service for purposes of the rule stating that a defined benefit plan cannot pay benefits until the earlier of retirement or separation from service. (I don't have a cite right now--does anyone on this board know one?) How long the person needs to be away before they can truly be treated as separated from service is unclear. However, it has been my experience that most statewide plans require at least a 30-day break in service. Given the lack of clarity as to the dividing line, being in step with other plans at least gives you some degree of safety.
Finally, what does the plan itself say? Even if the Internal Revenue Code would otherwise allow a distribution, a state or local governmental plan must also operate in accordance with its terms, and with applicable state and local law.