This is the problem. He didn't keep lead in sight. No excuse for not keeping lead in sight.
i've only ever flown formation twice in rl. both times i was the right seat pilot. both times we were the lead plane. it was only 2 plane formations. both times, we had specific procedures.
one of those procedures, was that if #2 lost sight they would go up and to the right, and we would then maintain straight and level flight. on the second time we did this flight, he did in fact lose sight of us, and informed us of such, as he went up and right.
this kept him away from us, and us away from him, as upon hearing that we maintained straight and level, until we both had vis on each other. the best part was that no one on the ground realized that anything was wrong up in the air.