From a strict point of view, death-bed confessions of faith are not acceptable. However, one might point to the thief on the cross as an example of one who was not baptized and yet will be with Christ in his Father's Kingdom when Jesus returns. That would be a mistake. When we read Romans 6 we understand that baptism is symbolic of death, burial and resurecction. Romans describes baptism as a crucifixion of the flesh. The thief was doing literally what we are required to do only symbolically! Jesus referred to his crucifixion as a kind of baptism. In Mark 16:15,16, the Lord tells us that whoever believes AND is baptised will be saved.
Having said that, the Father is quite capable of making exceptions to this rule. However, it would be foolish to presume upon His mercy and think you can sin now and say a quick little magic prayer at death and all will be well. It doesn't work that way. The Bible says that you reap what you sow. You cannot fool God or play legalistic games with Him - He will NOT be impressed with that kind of strategy.
Galatians 6:7,8 Do not be deceived; God is not mocked, for whatever a man sows, that he will also reap. 8 For he who sows to his own flesh will from the flesh reap corruption; but he who sows to the Spirit will from the Spirit reap eternal life.