Why didn't they kill Joe when...
They found Dekard's lair and kidnapped him.
He was obviously still alive, and the replicant was very forgiving.
I hope that wasn't a real dog - it would die.
Good question.
Seems to be they kept on underestimated him, is the suggested explanation. The assassin replicant underestimates him a second name later on of course, which leads to her death.
The other obvious explanation being is it's a film and they want the plot to carry out as planned.
Ya, I think the latter, and the producers think the mindless masses won't even question it.
Which they don't.