If one day you call to your guide and it doesn't answer, don't panic. Spirits have their own agenda. Odds are its off on its own business or is doing something that you asked it to work on. Some spirits are just not as active at certain times as well. An owl spirit might be cranky or choose not to respond if called upon at noon. The same goes for a bear spirit in the depths of winter. Remember spirits are not around to be at your beck and call. They are there to work in harmony with you and help you, not be slaves to you.
However if you feel that your guide is gone or if it hasn't responded for quite some time, think about how you have been treating it. Have you been kind and respectful, showing gratitude and affection? Or have you been demanding and ungrateful? Spirits, just like humans, have a habit of not sticking around where they aren't appreciated. If you have not been kind to your guide start calling to it and apologizing and mean it! They can tell if you are just trying to con them. Normally they will return once you have changed you attitude because for the most part they are very forgiving.
If you have always acted nicely to your guide it is possible that it is just on a long errand and will be back eventually. If not perhaps someone needed it more than you at this point in time or perhaps it is time for you to meet a new guide. Whatever the reason, be patient! Spirits work in their time, not ours.