This is not the last time the two heroes meet. There will come a time when Han So graduated and goes back to earth, only for the earth to be invaded by "alien" and Han So will literally die because the last enemy he will face on earth activates specific suicide explosion that only work on demon king Pedonar. Yes, Han So is mistaken as the resurrected Pedonar. What happen after Han So died? He reincarnated in Fantasia as a baby, and can keep his consciousness even from when he is just born to manipulate his physical growth using his black box skills. All of these happen and teaching staffs seems to unaware about it, even about the earth itself being invaded.
But hold up, before we talk further, there will be important arc between graduation and coming back to earth. When Han So graduates at round 6, he doesn't go straight back to earth. He will be sent to a dimension something like the event for hero alumnus where he meets the other ex-heroes. There, he reveals more secrets and the the truth about hero system and teaching staffs, and also that the Fantasia world the heroes sent to was just a replica of the real Fantasia. Due to him making chaos at the alumnus event, his graduation is revoked and he goes back to round 7. As we know already, he always try new things each round, but he graduates again and finally being sent to earth.
Ok let's back to after he gets reincarnated. The Fantasia where Han So gets reincarnated is where Sieg redo his hero exam. They later meet again to everyone's surprise, and face off against each other again.