Update: I read "original view" in the question as referring to the git blame view. If instead it is meant to refer to the source code file, then @statox's answer is the correct one.
I don't think fugitive provides a mechanism for going back to the previous blame view.
If you make a note of the buffer number before you jump to the commit (with commands such as
:echo bufnr("")), then you can jump back to it by passing a
count to the
:b command, but fugitive's mappings no longer appear to be set up.
You can make the hash appear in a split view instead of jumping to it by pressing o instead of Enter. (See