1) He will not run in 2020 (well, technically he is already running, but he will not be able to get a second term). He is going to resign or be impeached and convicted before then.
2) He would like a graceful exit, and early on I was hoping that for him, but the lies are just too much. He does not deserve a graceful exit. He hit the 3,000 lie milestone a couple days ago...these are public verifiable lies that he has told since inauguration day. As a contrast, Obama had 18 in 8 years.
3) I am not sure a graceful exit is possible at this point. They've just got too much on him. Might be some sort of plea at the very end so that he might escape prison, but he will be a disgraced President, and history will be brutal to him (deservedly so).