Council of Elrond

From the Fortress of Isen card:
"Other Fallen-wizards may not use the Wizardhaven card for Isengard"

What happens if I play Fortress of Isen while my Fallen-wizard opponent currently also has a company at the Wizardhaven card for Isengard?
Is the site card immediately replaced with a different version?
Do they keep the Wizardhaven version until they move (and then couldn't replay that version again)?
If they don't immediately replace the site, could characters in the company still heal at the Wizardhaven during their untap phase?
(I'm assuming strong no on that last one)

ICE wrote:>I have a question. If I have a character at the White Towers (using it as
>an unprotected Wizardhaven) and then my opponent plays Fortress of White
>Towers (or otherwise protects it), what happens to my character. It says
>no other players can use it as a haven...

You would have to replace the site with either the hero or minion version.

From other rulings, the site is immediately swapped out if something changes which site a FW would use.

And I believe that if their current companies would violate company composition rules when not at a Haven, the card giving the protection could not be played (err, technically, the declaration of play would be canceled?)