I reckon they go into storage! Have you seen how mega celebrities just randomly change the interior deco of their houses and just store all the rest away in a big warehouse!? I watched a reality show once and I think they we're refurnishing P.Diddy's crib or something... anyway... everything just went into storage! They should sell that stuff on ebay... imagine the listing:
"3 circular stages, as new, only used for one world tour, circus theme.... BUY IT NOW price... $10,598,432"