No doubt! There were even false messiahs in the first century A.D. and believers were warned of false prophets who would come to scatter the flock of God. The point is that Paul was not a maniac, mentally ill or misguided in his following Christ. He did so even though it meant "eating crow" and having to admit that persecuting Christ followers was wrong and he renounced it. He could have led a very comfortable and respectable life remaining a Pharisee and going after Christians - it was what the Romans even encouraged. He gave up EVERYTHING and often did without basic needs like food and shelter. He was beaten, jailed, shipwrecked - TWICE!, often earned money by doing menial jobs like tent making and waiting tables and he was executed in Rome.
So, either Paul was insane for putting himself through all that if it really wasn't true - and which case he would NOT have been accepted by the other Apostles nor given letters of recommendation and sent on missionary journeys - or he was really and completely changed by a miraculous meeting with the risen Christ. I just don't see how "ego" possibly fits into the story - he lost too much. So, which is it? Was Paul insane and he just fooled everybody or was he legitimate? Don't forget, he actually did miracles in front of people to demonstrate the power of God and to affirm his message was from God.
I have a relative that sits in a prison mental hospital today who believes completely that he is Elijah the Prophet and ALSO the newly appointed God the Father Almighty. HE is mentally ill - obviously. His actions don't line up with his delusions, but his mental illness prevents him from seeing what everyone else can. Paul was not mentally ill. Whatever delusions one may have to power and greatness - if it's false - it will NEVER succeed. Like you said, they end up getting killed. But Paul's ministry DID succeed. He led thousands to saving faith in Jesus Christ - probably millions, now, as his writings, as he was carried along by the Holy Spirit, speak to those whose hearts are seeking the truth. These words have POWER. The power was not Paul, it was Christ. Paul was chosen by Christ for a specific reason and NOTHING Paul did or said disproves this really happened.
Oh, look again at world history. Plenty of deluded men have risen to positions of power and most of them claimed to be some sort of direct link to God. Look at Mohammed. Now there is a success story that is still going strong, to the frustration of the civilized world.