Dear …
Thank you for your kind response to my Letter of Resignation. It is gratifying to hear that the talents I lent to __(name of organization/field/etc)__, were appreciated. My involvement with __(type of field)__ was rewarding to me in so many ways. I met many wonderful people that I now call friends, and I have also grown so much personally.
I do hope that I will have an opportunity sometime in the future to once again, contribute to __(type of field)__. There really were so many enriching experiences that I will always look back on fondly. At this time, however, I must take a break to attend to other things in my life. I appreciate your words of encouragement about my talents, __(name)__, and for leaving an invitation open for my return back to __(type of field)__. Thank you. For now, please accept my best wishes of success to you and __(name of organization/etc.)__.
Sincerely,