You mean plea bargaining? I don't think a solicitor could or would withdraw on that kind of strategy.
A solicitor would be required to resign if a criminal said "yes, I stole all this money, but I would like to plead innocent". Alternative, even without an admission, if a solicitor weighs up all the evidence against his client and concludes there is no prospect of a defence even though the client wishes to defend, he might step down on this basis.