A warning before deleting off screen content
Can't tell you how many times I've been working through a project, only to look back and see a large chunk of the project deleted because the in and out boundaries were selecting a clip and a vicarious press of the delete button ruins hours of work and forces me to open an autosave. some kind of warning, even one that has the option "don't show again" when something off screen is about to be deleted would save me that time necessary to fix the project.
While we wait on this feature, next best thing I can think of is having your edit "history" log panel open in the corner of your screen somewhere to see when edits are accidentally made (this unfortunate edit would is called "lift" in the history panel) You can also set how many edits you want to see in your history panel so in theory you could copy the sequence in the current state, back track the edits in the history panel and paste everything onto your sequence before everything was accidentally deleted.
John Wiley commented
Yes! Perhaps a dialogue something along the lines of:
"Warning: In point not selected"
Which would appear when you have only an out point set (so the in point defaults the to the start of the timeline), causing you to delete the entire timeline up to the out point (and usually you don't notice because it's off screen.
Peter C commented
I'm guessing the OP is referring to content on the timeline but not currently within the view of the current timeline on screen, ie before or after the section present on screen. Not content in the source bins.
This would be a useful warning, along with a similar warning if you are altering an effects parameters but the CTI is over a different clip. Been there, done that.
Mitch Wood commented
Do you mean a warning screen like the one attached? How are you deleting a file from your project that has been used in a sequence without getting this message?