The ending to "One Way Out" as done by the Allman Brothers Band has an ending that is common to lots of blues songs. It follows what sounds like a descending run like a normal turnaround with the ending being two chords with a beautiful minor/flat sound. What are these chords and how do they fit into the standard blues form? Here is the song.
This is indeed one variation of a standard blues cliché. The chords they play are
| A A7/C# D7 D#dim7 | A Adim7 A7 |
Note the chromatically ascending bass line in the first bar:
A C# D D#
which would often lead to an A7/E chord, i.e. the chromatic line would continue up to the E. The descending melody line you hear could be
| A G F# F# | E Eb E |
There is also a cliché melody line which would really descend chromatically from the G to the E (i.e., it would replace the second F# in the above line with an F), but it doesn't fit these chords. For that chromatic line to work you would need to replace the D#dim7 chord with a Dm7, which is one other variation of this classic progression.
This progression can be played at the end of a (blues) song, as in "One Way Out". With a slight variation it can also be played as a standard turn-around in the last two bars of a 12-bar blues. As a turn-around the progression leads back to the V7 chord (E7), which, in turn, leads back to the beginning of the next 12-bar verse/chorus:
| A A7/C# D7 D#dim7 | A F7 E7 |