Tragedy of the Commons does not modify any rules about how the card it is stuck to plays. Cards stuck to another card are removed from play when the card they are stuck to does.
1. Once the card is discarded, put face down in the stash, or unstashed and moved to your hand, it is out of play, and Tragedy would be discarded.
2. When a card leaves play, any cards stuck to it move to their owners' discard pile(s).
3. That is exactly how Silent but Deadly says it works.
4. Once Kaboom is discarded (which is the triggering condition for Forked!), Tragedy is discarded as well, see #1. Having already left play, Tragedy will not affect Forked! or the card it becomes.