There is already a warning when you remove a global variable. It states "any events tied to this variable will be removed"
On any moderately complex event sheet it's going to be quite difficult to definitively find where that might be, and sometimes the search doesn't quite catch everything.
It would be nice to have a list of events/actions/expressions that are tied to that variable presented when deleting.
Eg.
Global('MyVar') is used in:
Line 44 - if Myvar = 10 set text "You're FANTASTIC player!"
Line 230 - (Always) set myvar = 5