The cast of 'The Big Bang Theory' filmed their last episode on April 30. After 12 seasons and nearly 280 episodes, “The Big Bang Theory” is about to bid viewers a big farewell. And as is customary with any major hit, that raises questions about when — or whether — another network sitcom will blow up this way again. Chuck Lorre, who co-created the show with Bill Prady, has at times seemed like he’s single-handedly keeping the traditional multi-camera sitcom alive. In addition to producing “Two and a Half Men,” another huge hit for CBS, his credits include the returning “Mom,” as well as earlier shows like “Cybill” and “Dharma & Greg.”More recently, however, Lorre has migrated into single-camera comedies, including the “Big Bang” spinoff “Young Sheldon” — already renewed by CBS for two more seasons — and “The Kominsky Method,” the Michael Douglas-Alan Arkin comedy for Netflix, which earned the producer a Golden Globe Award in January.Despite his experimentation wit