If a coil can survive for an hour (say) being energized and not get too hot, there's no reason it couldn't be powered indefinitely. There's not really much to break in a coil; it's basically asking if it's okay to leave a wire energized for a long period of time. (A coil, after all, is just a long wire wound around a core.)
The relay contacts and mechanism can wear, particularly from switching under load, but steady-state operation again is not much of a concern provided it's properly specified for the application.
That's basically what Fred said in different words. I entirely agree with his assessment.
