Is actually not that bad if you have been using Time Machine as backup. Before upgrading, I made one last backup with Yosemite. To downgrade, backup one more time just in case, I also made a copy of all my important files on my external HDD, just restart your Mac and go into recovery mode, choose restore with time machine backup and click on the last backup with Yosemite. All went smoothly for me. I read the instructions through here http://www.techtimes.com/articles/90370/20151001/not-digging-os-x-el-capitan-heres-how-to-downgrade-back-to-yosemite.htm
Still we need a solution for El Capitan!
