Yes it must be distributed to participants, or used for expenses. Who gets it is another matter. If the plan was valued as of a certain date, and a participant(s) were paid immediately thereafter, then I'd argue that they don't share in the gains. If the money was invested and people were getting paid in dribs and drabs, then you have a mess because it wasn't handled properly. We* always quarterback the whole thing - tell clients to move to cash, do an interim val, and pay everyone asap thereafter to avoid this situation.
*Well, when I was in charge that's what we did. It's a bit more willy-nilly now.