Alert user before deleting symbol from artboard
Several times, I've accidentally deleted all instances of a symbol. When selecting a symbol from the artboard and deleting, it would be nice if confirmation were required before it deletes all instances of that symbol. If a user really wants to delete all instances, it's easy to do so from the symbols panel (right click --> Delete.) So I don't think this extra alert would be annoying, since the difference between deleting an instance and all instances is so subtle. When you are zoomed in close to just one instance and are on the layers panel (so you can't see the symbol in the library) if you've selected the wrong way and delete, you'll delete all of them without realizing it.
Jack Brind commented
I absolutely agree with this. My number one frustration with Xd! I have regularly 'deleted' a symbol from the artboard, not realising that I have deleted it from the entire project.