Without knowing the strength of the evidence against your friend, it's impossible to answer your question.
Your friend would be well advised to insist that his solicitor arranges a conference between the two of them and his barrister. Solicitors and barristers often see cases differently but the barrister will have much greater knowledge and experience. He will be able to give your friend a good indication of the likelihood of acquittal if he pleads not guilty.
It's far better that your friend speaks to the barrister directly, rather than through his solicitor, which is why I suggest that he insists on a case conference.
Chris