If you build a card bell tower, the game can be completed after the 7th turn. Can somebody destroy the bell tower with armory, after he build the seventh card? And if it can be destroyed, is the game over anyway?
According to all the FAQ's I have seen the armory can still be used to destroy the bell tower after the 7th district is build since the card does not disallow it like the warlord does. While the warlord says 8 districts it must be remembered that the bell tower modifies the rules to change winning from 8 to 7 which would also change what is on the warlords cards. However even if you do destroy the bell tower the game would still end as the end game condition is triggered when it is met not at the end of a round.
From the rule book.
When a player builds his eighth district, the game ends after the current round is completed.
This rule does not care if something happens after the victory conditions are met but just that they where. And in this case the conditions where changed from 8 to 7, they where met and then later changed.
Also from the official FAQ
Q: If the Bell Tower is in play, can the Warlord destroy someone’s seventh district?
A: No. The Bell Tower makes a seven-district city “completed,” and the Warlord cannot destroy districts in a completed city.
Q: How do you handle the endgame scoring bonuses when the Bell Tower has been built?
A: The bonuses are awarded for seven districts instead of eight. If one or more players have seven districts when the Bell Tower is built, they all get the four bonus points for simultaneously meeting the seven district condition. If the Bell Tower is built as someone’s seventh district, he and anyone else with seven districts get four bonus points for simultaneously meeting the endgame condition; any players to subsequently reach seven districts before the round (and the game) ends get two bonus points.