It actually lasted quite a while. I went travelling for a bit, and when I returned it was still there. But then I left it again for a while and upon my next return it had glitched through the walls and was butchering the farmers. When I loaded my save back... it was gone.
That is obviously not the intention of the person that made that video. Your suggestion just shows that you didn't even watch the whole video before commenting.
I watched the whole video, I'm just saying that it would be more useful dead. His settlers would probably never stop trying to shoot at it through the walls.
You can have a settlement without any settlers in it, you just have to not put a recruitment tower in it.
Also getting a legendary item vs doing something for fun are very different things. I know that after spending over 70 hours in F4, I don't really give 2 ***** about legendary items anymore.