They'll have their ups and downs, but Babe Ruth will always be popular and continue to rise over the long haul. Especially as it continues to get harder and harder to sell forgeries. But whether Ruths will be higher or lower a year from now, you never know.
As long as baseball remains a popular sport I can't see declining interest in Ruth. While baseball may not enjoy the dominance it once had, it is still very popular. In Latin America and obviously Japan baseball is still king. So, global growth will ensure demand continues. IMO, baseball is safe for generations.