Originally posted by Grille
Welcome to CFC, Sentinel
in addition to Turner's post:
Strategic resources never disappear if there's no road (respectively city) on that tile. (Maybe you would not want to connect your only source of a resource before you really need it, or even disconnect/pillage roads if you e.g. notice a Iron Works city site but can't start IW right away).
Rubber and horses a "static", they will never disappear (as Turner said, check editor for depletion odds of the rest in the editor).
Correction: If a resource is attached but the road cut, the resource is still eligible for depletion. Have to look this up, but I'm pretty sure it's still that way.