Apple - Copy to clipboard from Tmux in El Capitan
Actually, I just find out very simple solution how to enable copying using Cmd+C again.
In default Terminal application go to View->"Allow mouse reporting" and uncheck it. Thats it.
PS: Obviously, the new nice features like dragging split screen in tmux stop working after unchecking the mouse reporting.
If you use iTerm2 3.x, you can make copy / paste work by enabling
Applications in terminal may access clipboard:
Just highlight text with your mouse to copy it into the OS X clipboard!
You can also paste from the OS X clipboard into tmux with the usual Cmd + V.
If you hold the function key down you can select and copy to clipboard with apple+c as well.