Technically (under the hood) it is not deleting them. It is placing them down, and then overwriting them with the next clip. That is why camera 3 survives. Camera 1 is placed. Then it is replaced with camera 2. Then camera 2 is replaced with camera 3.
This replacemnt can also happen if you just leave a random clip on the timeline (without selecting for alignment) and then one of the aligned clips is placed on top of it.
I am not sure if it is worth the effort and complication of adding the warning. This is a bad practice. Each camera angle should be on its own track. I have already written this into the documentation:
Anyone who does not read the documentation will soon learn it for themselves through trial and error. In case someone does not put each camera on its own track, then can use “ctrl-z” to undo the alignment and get their clips back.
Done
We could add Ctrl+Shift+R and Alt+Shift+R, but those are not actually “options” like the other entries in that sub menu. They are convenience actions to toggle multiple options. For that specific menu, it might make more sense to add Ripple (Ctrl+R) and Ripple Markers (Alt+R) since those are individual options.