I just want to know did she say yes
No, she threw the ring on the ground, kicked him in the face and ran away. He was heartbroken, tried to commit suicide and the aliens rescued him again. Now he's living in their version of a zoo as their most visited exhibit.
...
It's implied that she said yes. Did they live happily ever after? No one knows, then again if you keep going with a story long enough you'll witness the heat death of the universe. So they probably did not live happily ever after.
That's what happened in my first proposed extended ending.
Okay, I'll stop making stupid jokes.
As it is the ending is [SPOILERS AHEAD]:
"The screen door opened, and Scott waited for his future to say yes."
It's a good ending point and just adding on more would make the story worse.
Both "Human Man" and "Human Phoenix" are about Scott growing up and becoming human. The culmination of it all is him deciding what he needs in his life and actually asking her to marry him. The answer itself is not the point, it's about Scott and his journey.
After the way she pursued him, does anyone here actually believe she would say anything but 'Yes!!!'?
And I agree with Oyster, unless you bring the aliens back, the story arc is pretty much completed. The tension is resolved, and only some petty details left to be completed.
Or you could do the last half of rlfj's story about Carl Buckman and tell how he became Congressman and President of the United States and changed the world.
A Fresh Start is about changing the world to fit the hero. Human Man is about changing the hero to fit the world.