timing, storm castle?

[Merry Jolkar]

I have just knocked down the walls of the Machaka Lich Lord's Mausoleum. If I now storm the castle, and he sends his large army into the province from next door, will I:

1) fight the Lich Lord and then own the mausoleum, which will defend me from the large attacking army

2) fight first the large army, then the lich lord

3) fight first the lich lord, then turn and face the arriving army?

Also, once I kill the lich lord in his home province, does his army disappear ala the orc hordes who vaporized after Sauron was killed, or do they remain, but leaderless?

Thanks!
Merry