Thinking of watching 86 but before I start:
Part 1 adapts the entirety of the first volume, while part 2 adapts the 2nd and 3rd volume.
There are currently 10 volumes released and the story is ongoing.
As for your second question, it's kinda complicated. The story was originally going to end on volume 1, but the author won an award and decided to continue the story. So, in a way, you can take part 1's ending as an ending to the story, but that's not recommended, because part 2, especially episode 22, is peak.
Also, the anime doesn't offer an original ending, if that's your question. It is completely loyal to the LN and is considered to be one of the best recent LN adaptations.
The last episode's not released yet, but I don't think it's gonna end on a cliffhanger.