- Magic can be cast outside the castle, but it won't be able to affect the castle. Things like portals or spells aimed at the doors would be absorbed.
- The blockade blocks all magic abilities from the outside, so they would not be able to.
- Yes, they would be able to pass messages underneath the door provided they have ink and paper.
- They would find the king was no longer in the throne room. Other attempts to find him would also prove fruitless. The guards that were in the throne room have disappeared as well.
- All windows, doors, etc. seem sealed shut. Any attempts to smash windows just bounce right off of them.