The A300/310 is a goner, for passenger services, that is. Not because the 200-250 pax-segment becomes less popular, but because they become older and less economical to fly. I think their routes are taken over by all kinds of aircraft. Most airlines substitute their aircraft with a mix of narrow-bodies and bigger widebodies. American for instance, can easily replace the A300 on its routes by a mix of 763s and 772s. Swissair replaced their A310s partly with A320/321s, and partly with A330s. KLM replaced theirs with both 763s and 733/734s. Thai just received some A300s so they might fly some time with it. Singapore replaces theirs with a mix of A340s and 777s. They hardly have low-density routes so they don't care for narrowbodies. And don't forget the A300-600 and the A310-300 are still quite modern, it will remain popular with airlines who fly long thing routes and can't fill jumbo's (like TAP, Royal Jordanian) for some time.
The closest thing to the A300/310 might be the A330-200 which is about the same size and has a lot better perfomance, and sells nicely.
nobody has ever died from hard work, but why take the risk?