In the US at least, there's typically a presumption of survivors. One benefit to this is it provides "real-world" training (even if everyone's dead) - collapsed

In the US at least, there's typically a presumption of survivors. One benefit to this is it provides "real-world" training (even if everyone's dead) - collapsed buildings are especially difficult/expensive to simulate. Rescuer safety is the major variable in deciding how much time and effort to put in. So you'll see searches continue for an "unreasonable" period of time, both because people seem to survive in unreasonable circumstances and also because you've already got everyone out there - but once the weather turns bad, they'll usually start scaling it back or call it off (unless there's high confidence that something specific needs to happen in a specific area). USAR teams have a variety of listening equipment to attempt to localize victims in a collapsed building, and while that ability could definitely be improved, I'm very skeptical that sending in a bunch of cockroaches to crawl all over people pinned in rubble is the best we can come up with.