Yeah for me it was a series finale as well. A grim one, but it's a good end imho.

I find that difficult to believe. Seems to me that a lot got settled.
Cooper's death was to me basically "Live by the sword, die by the sword"
He had his demons, was getting progressively darker and was never going to find peace. He went out with a bing, literally, and not with the whimper of so many others.

Never give up on a movie being from this show but it would take a Studio Executives to take a bit of a gamble and investing a limited budget on it but it is doable.
However if you want NEARLY the movie form of
Southland
then just watch
End of Watch
. The movie is realistic and authentic because of Director David Ayer and his Police Technical Advisor Jaime FitzSimons. It actually contains many actors from
Southland
such as Cle Sloan (Ronnie), Maurice Compte(Officer Rodrigo Morales) and Richard Cabral (Leprechaun).
If you are not willing to give up everything, you have already lost

I responded in a different thread with this:
The show never got to have a series finale. What you saw was a season finale. The show was cancelled and what happened at the end was never resolved.
For what it's worth, Michael Cudlitz said that
his character did not die.
He's like an idiot savant, minus the savant. - Tom Servo

Both what was on the aired episode on TNT in 2013 is the exact same as what's on the DVD. Both show Cooper getting shot 2 times to the centre mass. It wouldn't be much of a cliff hanger if it didn't show him getting lit up by other patrol Officers!
If you are not willing to give up everything, you have already lost