[Ryanamur]

First part, you can get out of Skull Castle using one of the 3 following methods:

1- If you create a portal before you passed the gates, just teleport out of that area.

2- From the ball room (the room with the stairs just on the other side of the gate), just jump and climb on the balcony. You need high agility and to be unincumbered to do this.

3- From the bridge, you should be able to get out using one of the four pathways (memory fails if which one if any)

For the second part of your question you can get the key from the Litch (you can also come in from the back door through the maze... accessed from jumping off the bridge)

Cheers and good luck.