If you turn off of any type of avatar (or all at once), then they will still be displayed at the forum and in the profiles of users using a disconnected type of avatar, although the settings are:
If you disable avatars in general or avatars of a certain mode, the disabled avatars will no longer be shown on the board, but users will still be able to download their own avatars in the User Control Panel.
In 3.0 it worked properly, but was broken in 3.1.