If such a feature is implemented, it should give the OP the option to also lock their progression thread, preventing the addition of new posts, when they mark it as dead.
I made the mistake of posting an update in one my progression threads to let anyone following know that the tree had died. Despite specifically stating that I really wasn’t looking for a postmortem discussion, that’s what took place in the thread. It’s one thing if you have a tree die and you don’t have any insight into why and actually want community feedback. It’s quite another thing to have a pretty good idea of what killed the tree and to get unsolicited advice after specifically stating you don’t want it (including advice that assumes you made amateur mistakes that you didn’t actually make). Back seat driving when the car has already crashed can be quite obnoxious.