At about 48:10, someone asked what happens when a living person in a Family Group Tree is marked as deceased. The answer is simply that it works exactly like it does when you mark a living person in your private tree as deceased. The profile becomes part of the shared public tree, and within the FGT, all relationships to any living persons in the FGT are preserved. Of course, that same person may be marked as deceased from within various private personal trees, or from within other FGTs; all of those would then be public and would need to be merged together. If you need to undo it (because the person is not actually dead) then you need help from Support, exactly as you do for people incorrectly marked as deceased from a private tree.