OTHER FIZZLED FESTS: With thin margins and a challenging economy, some summer festivals have already begun to disappear, Sisario pointed out. Among the casualties for this year are Rothbury, a two-year-old event in Michigan also co-presented by AEG, and Pemberton, near the site of the Vancouver Winter Olympics, which took place in 2008 but has been on hiatus for the last two years. (2/24a)