How can I disable plugins but not delete, is it really not possible for all bai?

You can disable plugins on a per layout basis. Edit a layout and go to 'details' where you will see a list of 'gadgets' that can be enabled/disabled for that layout.

I'm not sure what you are saying/asking. But I'll take a shot.

If the plugin is not listed on the 'details' of the layout and does NOT show up as an area when you edit a layout then the only way to "disable" it would be to uninstall it. This is because, the plugin is made to load all the time instead of being added on a per page/layout basis by the user and therefore, is either ON all the time OR 'off' all the time (which means uninstalled)

I looked at the "Simple Gallery Extended" plugin and it loads all the time. This means that the creator did not give the user the option of using it on a per page/layout basis and therefore once it is installed it will always be "ON"