It can't be a fan continued game... give that thought up. TLG owns all the content and we all signed a users agreement. The NDA for employees being up will only allow them to talk about ideas, not implementation.
Unless someone purchases the rights to LU, NONE of its content may be used. not one iota.
Most game studios retain the game assets and code, so technically it will be preserved within the LEGO company, however with MMOs the only way players can still play it after it's released is if the source code is leaked/stolen or reverse engineered. As far as I know no company has ever released the source to their MMO, most likely because of millions of dollars invested in making the technology, which they wouldn't want competition to get a hold of for free.
It would not be legal, unless you purchased those rights from LEGO.
However, enough attention might cause a revival by TLG or purchase of rights by another entity.
