In order to reply to a goodbye letter, you must first touch each and every point which was mentioned in the letter written by the other person. Make them realize how much you care about them and that you remember everything that they had to say.
Start off by inquiring about their health and then get to the point where you want to say goodbye to your loved one.
Sample of How to Reply to a Goodbye Letter
Number 4 Public Road
I hope this letter finds you in good health. Last night I got your letter and it shook me to the core that you were leaving the city forever.
We have spent a long time together and I believe saying goodbye is extremely hard. Your letter made me fall to tears because the connection and the bond that the two of us shared is just like two brothers. You wrote in detail about a few things which you cannot forget and with each and every passing minute your letter gave me Goosebumps because it took me to a trip down the memory lane where I could remember everything that we did together.
It has been 13 years and now saying goodbye sounds difficult. I simply could not comprehend that we will not be seeing each other anymore. But I am glad that you have looked for opportunities outside these borders and they it is going to help you out in your career. I am happy that you have an admission in a credible institution and I really hope that you excel in whatever you do.
I would only like to tell you that I have always treated you like a brother and as much as it has come to me as a surprise; you leaving makes me happy because this gives you the opportunity to grow and I am extremely happy for what you have achieved over the years.
Take care, Johnny, and I hope to remain in touch with you.
Your friend forever,