So, this item came up last night while we were playing. I'll give you our answer, but I want to see what everyone else's thoughts are.
One player was playing as Abu Simbel, and their neighbor had the Courtesan's Guild in hand. They asked whether they could "use" an "Entombed" Leader, or what would happen if they used a Leader that was later "Entombed." We decided that they couldn't use one that had already been entombed, but if they used one that was later entombed, they would not lose the benefits.
Does this seem appropriate, or should we have gone a different route?