Thank you for this lengthy explanation. Others have also tried to explain things to him but when the heart is sealed, it is sealed. If I took him seriously I would have argued that Allah, Heaven, Angels, Hell, Shaitan, Grave are among a few things other things that are ghayab.
The Prophet (صلى الله عليه وآله وسلم) was in occultation (ghayab) the first 40 years of his life; he was in occultation during hijra and even left a naib in his absence.
Furthermore, Allah promised Hz Ibrahim (عليه السلام) that Imamah would be in his progeny. There was no caveat about Hz Ismael (عليه السلام) or Hz Ishaq (عليه السلام) only inheriting this responsibility neither was there a term limit on how long this would hold therefore Imamah would be in the progeny of Ibrahim until the end of time.
With that said, Imamah ended in the progeny of Ishaq with Hz Isa (عليه السلام) who didn't die but went into occultation - Allah kept his promise. Similarly, the promise in Ismael's progeny couldn't end with the Prophet (صلى الله عليه وآله وسلم) because he was martyred. The rank of Imamah continued through Imam Ali (عليه السلام) until the 12 Imam who also went into occultation like Isa - thus retaining Allah's promise to Ibrahim that Imamah would remain in his progeny until the end of time.
BUT I can't take @sunni muslim seriously so I choose mockery.