You really have no clue what ELECT means, do you?
"But you do not believe because you are not of My sheep." [John 10:26]
Q. ... but what if someone that was not one of his sheep believed?
- A.: It can't happen. The reason they do not believe is BECAUSE they are not one of His sheep.
"My sheep hear My voice, and I know them, and they follow Me;" [John 10:27]
Q. ... but what if one of his sheep did not hear Jesus?
- A.: Then Jesus lied and we are all still dead in our sins.
Q. ... but what if Jesus did not know one of His sheep?
- A.: Then Jesus lied, God is not omniscient and we are all still dead in our sins.
Q. ... but what if one of Jesus sheep refused to follow Him?
- A.: Then Jesus lied and we are all still dead in our sins.
However, one of Jesus' sheep can wander away, and in that case ...
3 So He told them this parable, saying, 4 "What man among you, if he has a hundred sheep and has lost one of them, does not leave the ninety-nine in the open pasture and go after the one which is lost until he finds it? 5 "When he has found it, he lays it on his shoulders, rejoicing. 6 "And when he comes home, he calls together his friends and his neighbors, saying to them, 'Rejoice with me, for I have found my sheep which was lost!' 7 "I tell you that in the same way, there will be more joy in heaven over one sinner who repents than over ninety-nine righteous persons who need no repentance. [Luke 15:3-7]
"and I give eternal life to them, and they will never perish; and no one will snatch them out of My hand." [John 10:28]
Q. ... but what if someone that was not one of his sheep and given eternal life later perishes because they were snatched out of His hand?
- A.: Which part of "ETERNAL" is temporary? Which part of "NNE" really means someone?
To answer directly, failure to persevere indicates that Mr Harris was not one of the elect. I quoted from the place where John offered the exact same message ...
"They went out from us, but they were not really of us; for if they had been of us, they would have remained with us; but they went out, so that it would be shown that they all are not of us." [1 John 2:19]
Don't you accept John's answer to your "what if" questions? (Calvinists do.)