Do people have to be physically in the US when green card is app

Dear PJ and other experts,

I've become a US citizen and am now trying to apply for green cards for parents. They are here in the States as visitors.

I'd like to submit advanced parole request along with I-130 and I-485. Assuming that we'll get their advanced parole before their I-485 is approved:

(1) Can my parents safely go back to China and come back later on the advanced parole? (My guess is yes.)

(2) What happens if their I-485 is approved during their absence? Is it still valid? In other words, do they have to be physically inside the US when I-485 is approved?

(I tried to checkk on PJ's blog but didn't seem to find the info.)

Thanks!!