Let's say I am a vampire who has been around for thousands of years and that I am a 20th level wizard. What can I do to make sure that I am never permanently destroyed.
I believe that it is possible to have more then 1 coffin but you can not use just any coffin. As such I would have 2 or 3 hidden in every small city or larger in the known world. They should only be accessible with gaseous form. Setting these up an maintaining them would be difficult since there may be several hundred to a few thousand coffins. A simulacrum would be able to cast teleport so this would able to arrive in a new city each day and do any needed maintenance. A permanent telepathic bond would allow contact and with its nightly travels could keep you well informed on the world situation. A second could do the same thing in you actual operating area.
I would keep my main coffin in lead lined airtight room deep under the earth. Not sure of the best ways to do this but I would make this room not conducive to life. I think a juggernaut in a room with lightning traps would be a good way guard this coffin. Put the coffin itself in a admantine safe and embed in it with in the floor of the room. Cast non-detection on everything in the room everyday. Cast getaway before you leave this room each day and so that even as a gas you can get back.
Mage's magnificent mansion should be cast everyday and a coffin kept there as well. A coffin can be carried with you at all times with the help of shrink item and permanency. Contingency with plane shift gets you back to the material plane.
On top of all of this I would create two demi-planes. One to astral project out of and the other store a clone. Guard both a juggernaut and give the plane negative and timeless traits. Limit magic to wish, plane shift, astral projection and few nice battlefield control spells that will be permanent due to the timeless nature of the plane. Cloud kill is a good one as is blade barrier but that would need the help of a cleric to cast.
With all of this you would need to know about kill two bodies on two separate demi-planes and the astral body is hard to kill due both a teleport and plane shift effect.
