So what do you do with a used writ of lease once you’ve used it to place a plot on New Magincia?
You can keep it. You can sell it, you can toss it in a trash can, you can keep it with the house and if you ever get rid of the house, give it to somebody as a souvenir, or keep it as a souvenir yourself.
In this Stratics thread, Phoenix, aka Mike Moore, UO Systems Designer, reaffirmed this, mentioned the original New Magincia document pertaining to it, and stated this:
The expired writ will not be deleted. It’s a normal blessed item, and can decay or be lost like any other normal blessed item, but it won’t just vanish after 30 days.