McClellan would have been inaugurated in March 1865. Lee would have still been penned in Petersburg. Sherman would have captured Atlanta, or bypassed it and gone on through Georgia, or surrounded it and penned in the rebel army. In any scenario you care to mention, the Confederates would have been on their last leg and barely standing. You really think McClellan would have snatched defeat from the jaws of victory and surrendered to them under those circumstances?
Where did I say anything about surrender?