"Dash" left last year, when Jay-Z was promoted to president of Def-Jam Records.
For all my research I can find no information of 50 cent's involvment in Roc-A Fella Records. It's not really owned by anyone now, it's just part of the Island/Def-Jam Records catalog.
Jay, Dash and Kareem "Biggs" Burke, were the founders.
wikipedia, while being one place that you have to watch out for has a decent track record with entertainment related articles.
http://en.wikipedia.org/wiki/Roc-a-Fella_Records
Hope this helps.