If the crankset has been treated well and kept snug, the crank will stay seated. The triangular axles hold the cranks so firmly that once pushed on by hand, it's difficult to remove them. I think many got damaged in the process of trying to disassemble the bottom brackets because of the tight fit.

Here's an axle/BB assembly, with the alternate axle bolt referred by T-Mar and an older Flyer crankarm