If you say “No” does he go away forever??
(Pic taken from YouTube video)

I’ve spoken to him at Silph Co. and said no, cause I didn’t have a forretress, but now I’ve got one, he isn’t there!

I’ve done the copycat quest,
I’ve been to the pewter city museum and spoken to him there before (he’s not there now)
I’ve beaten Red,
I’ve already taken the Hoenn starter from him,
I’ve caught Latios (SS)
I have a National Pokédex

Where is he?! What do I do?
I want that beldum!