Various different factual works have specified that at some point, The Motion Picture was supposed to end with a battle between the Enterprise and a set of Klingon ships. Maybe it was just a broad idea, maybe not. But one thing we do know is that Andrew Probert went as far as providing a few sketches on how this could come about (including a sequence where the 1701-refit undergoes a saucer seperation).
From Memory Alpha
a saucer separation involving the refit Constitution-class Enterprise (NCC-1701) was story boarded by Andrew Probert for a possible scene at the end of Star Trek: The Motion Picture.
The general gist of the scene was that the saucer section would fight alongside the drive section, evening up the battle against a small Klingon fleet (a bit like the way the USS Prometheus was later designed to do in VOY's "Message In A Bottle").
Do we know if this sequence ended up in any actual draft scripts
for the film? Or was it only ever a conceptual idea, never getting green-lit or as far as being scripted?
I was thinking about it the other day and was trying to figure out how it could have been included. I doubt it'd have been a seperate fight at the end of the existing story, because it would just feel tacked on. Is it possible they considered making it so, instead of being destroyed at the start of the movie, the three Klingon ships are instead swallowed by V'Ger, like the Enterprise is? And when V'Ger is defeated, it regurgitates the Klingon ships in orbit of Earth, leaving Enterprise with the problem of three angry Klingon ships?
On reflection, it might have made for a stronger film if the Enterprise had encountered the Klingons inside
V'Ger. And they all had to work together to uncover the secret of how to escape. It'd certainly be a very Star Trek idea, even if the Klingons then became turncoats when they all got out of V'Ger, and opened fire on the Enterprise again.