I actually never gave a second thought to what happened to Ruth, and apparently neither did old Rose in the movie. After debarking from Carpathia, Rose eventually gathered enough money (without selling the necklace, as that would've been a huge spotlight to where she was) put distance between them, ending up in California, the movie industry, etc. I'd say that she met Ben Calvert either through the movie industry or shortly after her star dimmed some (she was likely more popular in silent movies than she was in "talkies", as happened to a lot of actors of that time period). I'd say that Ruth ended up in the profession that she was afraid of ending up in; seamstress. Also likely died poor, since her meal ticket out of debt was dead (in name only, of course).