I personally don’t believe the whole truth can or will be found outside of the Church. Simply because the head of the Church is Christ and Christ is the Word of God. However, this is not to say I believe that those who are not Catholic/Christian will not find truth. Also, the members of the Church only know that truth which has been revealed to them by God, and no more. Think of the Mysteries of the Rosary. They wouldn’t be Mysteries if we understood them fully.
This is of course a very shallow answer to a very deep question. My opinion: a truth cannot be found that will be in contradiction to a truth established in the Church.