I'm not sure if you are asking from the perspective of a participant or an plan sponsor.
If you are a Participant, the summary plan description (SPD) can provide you with the terms under which distributions can be made. The SPD is a booklet that describes the plan's provisions and the participants' benefits, rights, and obligations under the plan. You can obtain the SPD from the plan sponsor (the employer).
If you are asking from the perspective of a plan sponsor, you might be better off freezing the plan to additional participation rather than cashing it out because cashing out or liquidating a plan requires that the participants be immediate vested.
I hope this helps a little. I can answer more specifically if I have more details.
I can be reached at 908-821-9764 or email@example.com if you would like to contact me with the details.