due to the change in the structure of the website I by mistake deleted the blog folder from my control panel directory. Now I want to retrieve these posts back along with all the comments that I received. How can I do it?
All data is stored in your database. Just upload the files back and set up your config file as it was before. It should work fine then.
"Imposter" is right all the data is stored in your DB. you only lost theme/plugin modification (if any) you have made.
As it sounds like you didn't have a backup for files you can only hope the database still exsists so export it and then set up your blog again adding all plugins and themes you had before. This way you should be able to rebuild your site.