I play M campaign. And, since the AI doesn't recruit as much as on VH level, it's not necessary in M campaign to pursue and kill all enemy routing troops. You can afford to do the historical thing and let some of them escape.

I don't pursue with exhausted units, and I don't pursue at all with hoplites or phalanxes. Pursuing routers is a job for light infantry and light cavalry, and even then it's only worthwhile when there are a lot of routers. If there's only half a dozen left from an enemy unit, it's not worth the effort of pursuing them.