If teenagers (and their adult supporters) were really concerned about what they'd miss if they died today and making sure that their wishes about their death are respected, they would not be hashtagging "If I Die in a School Shooting" but rather "If I Die in a Car Accident," as the latter is the leading single cause of death among people aged 12-19. (Yes, this is the latest data I could find.)
Car accidents account for 35% of deaths, with homicide overall at 13%, and only a fraction of that 13% is accounted for by school shootings. Kids are FAR FAR more likely to die in a car accident than at school.
And ending the War on Drugs would do far more to drop the teen homicide rate than any other single policy.
None of this is to say that we shouldn't see what we can do to reduce the number of school shootings, but responding responsibly to that problem means not giving into irrational fears.
You want to save teenagers lives? Take away their phones when they drive and put your phone (and your drinks) away too.