(Quoting from the English rules, from the [linked PDFs](http://boardgames.stackexchange.com/a/10939/3532).)

*Cities*, page 5, about **Diplomacy**:

> A player who puts into play a card with the [Diplomacy] symbol takes a Diplomacy token from the bank and places it on their board.

*Cities*, page 8, about **Aspasia**:

> When Aspasia enters play, the player takes a
Diplomacy token.

*Wonder Pack*, page 1, about **Abu Simbel’s stage 3**:

> The player can no longer benefit from the chosen Leader’s effect.

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I’d say **the Diplomacy token stays on your board**. After bringing Aspasia into play, the Diplomacy effect gets exectued instantaneously, leaving Aspasia with

* a now useless Diplomacy effect, and
* 2 VP at game end effect

both of which stop being active by burying it. But this doesn’t affect any benefits this Leader gave you *before* burying it, and it doesn’t require to rollback anything made possible by this Leader.

Think of the other Leaders: Many of them also have instant effects, like Caligula, which allows to build one black card per Age for free. If you’d use its effect and bury it afterwards, you wouldn’t have to get rid of the black card in retrospect.