Mongolians for ever

[Shahed]

Mongols, Turks, & Timurids ARE FOREVER !!!...
...followed closely into eternity by the Egyptians and the Moors !!!

[Kommodus]

Hm, I was under the impression that a siege battle would end if all siege equipment was destroyed with the attackers still outside the city. Is it possible to destroy ladders?

Other than that:

1. Turn the time limit back on; it really does give plenty of time to fight battles.
2. Lure the attackers close to your walls by launching brief sorties with cavalry. That should give you a chance to kill the rest of them.