All the return to Israel stuff I've read in the Bible was concerning the return from Babylon, which was their immediate concern at the time.
Considering that they were in exile themselves, even if they knew about the future diaspora it'd be way down the list of their concerns until they sorted...
Paul took it to the genitiles, Peter took it to Rome, Constantine made it the official religion of the Empire, invading German tribes became Christian to become more Roman, England became Christian, Christian English people went to America and voila!