One common myth about hypnosis is that you won't get out of the trance or that you'll never wake up. This just isn't going to happen. If for some reason your subject falls asleep and no longer responds to your suggestions, you can just wake them like you would any other sleeping person. Or you can let them stay asleep and they'll wake up later as they would out of a nap.
There are a lot of ways to pull someone out of hypnosis. I will describe two ways for you and through experimentation you will work out which to use when.
In general you pull someone out rapidly in order to create an open loop. You do this by not finishing the hypnosis session and part way through the experience breaking the trance. For example you might be having someone describe their new found confidence to you and partway through you wake them.
This leaves them in the state of mind of seeing themselves as confident. You can close the loop hours, days or even weeks later. The lessons learned from the loop will be far more lasting than if you just closed the session. I usually break the trance quickly by saying "3,2,1 awake!" really rapidly and the person wakes up almost instantly.
The other way to break the trance is by creating a trigger that's linked to "waking". This trigger is a hypnotic suggestion that is going to take effect only after they wake up. As an example you might say "when you awake you are going to feel a surge of confidence. This will improve your mood and make a lasting impression on how you see yourself."
To break the trance you count them out of it slowly. You introduce the idea by saying "I am going to begin slowly counting to 10. With each number you will feel yourself gradually becoming more awake. With each number you will feel your confidence rising. With each number you will begin to feel better about yourself and what you are capable of. "
Then you begin counting, with each number adding a suggestion.
For example, "One, starting to awake gently."
"Two, begin to feel energy returning to your body."
"Three, the increased energy is already improving your mood and making you feel better."
"Four, you almost feel as though you can open your eyes."
"Five, you can feel the effects of the hypnosis session beginning to have a powerful and positive effect on your life."
"Six, You can feel a surge of energy rushing down to your feet."
"Seven, you are starting to feel awake and full of energy."
"Eight, as you begin waking you can already start to notice how the lessons from the hypnosis session are improving your life."
"Nine, almost there, almost completely awake."
"And ten, open your eyes, refreshed and wide awake, ready to enter the world as a positive and confident person."
Each of these two methods have their benefits and with practice you will learn when it's best to use each one.