For a definitive answer you should contact the SS administration. However, I know of no reason your SS# wouldn't be valid and would be very surprised if that wasn't the case. SS#'s are assigned for life (forever?) and there is nothing I'm aware of regarding movement in and out of the US that would invalidate your number.
But to be sure, contact SS directly with your question.
Numbers is hard.
The problem with the world is that the intelligent people are full of doubts while the stupid ones are full of confidence. - Charles Bukowski
Retired in 2005 at age 58, no pension