a) Usually by request and usually requires requests from multiple individuals.
b) Treads have to either be turning towards vitriol or are already there.
c) Threads are rarely retired completely, what happens is they are turned into a thread like exists almost every other message board system. Meaning they are pigeonholed.
d) So in this case, you click on Index and scroll down to 'Sidelined' there it is. Its just that it will not come up through the RagePage or Nu2u for those logged in. (it may be inaccessible for those not logged in, I'll have to check)
All sidelined does is take a thread off the front burner. If you reply to it, it still sends an email to anyone who subscribed to the thread.
PS I love that thread.