The sell mode has always been there and without it the game would be impossible to play.
There have been recent changes to the design of it, so those could be reverted to the old version, but what you describe has happened also before this change, so I don´t think there is much in the way of improvement even reverting to the older version.
AS
@Silly Bubbles said, some buildings can be replaced, especially event buildings, so your ferris Wheel can be restored to you if you contact support, if you meet certain criteria. AWs however will not be restored, so the GA has no chance to be restored other than a christmas miracle...
I believe it is possible to switch the confirmation message on and off, so check your settings there, but even with the confirmation message active, we still tend to ignore it and click too fast lol, so that´s no real fail safe either.
Other have suggested an "undo-button" you can find it if you look through the suggestions section.
So your problem is a common one, so far all we can do is live with the occasional misshap. One of my fellows just deleted a high level FA, but luckily she´s a hoarder and can rebuild it quickly. But a solution to a very common problem would be appreciated by many. One can hope ...