I think it is quite a stretch, the Civil War and WW2 didn't stop presidential elections. It's hard to imagine what kind of excuse Trump could dream up that would justify postponing an election.
The excuse he threatened not so long ago was over his wall funding. He conceded he would probably be overruled at the 9th circuit but pondered if he could be successful at the SCOTUS. I seem also to recall him speaking to a room full of his nitwit MAGA shirt wearers that he could overturn the two term policy. He sort of appeared to be joking but I'll venture a guess his ego would be sufficient for him to give it a serious try.