As I've said, I can't see Trump being in office for 4 years. Whether or not the world would be a better place with President Pence is debatable.
I don't see anything bringing down the administration, no matter how horrible or corrupt, even if Dems take power in 2018/2019. I just think Trump gets more and more miserable, spending less and less time at the White House, but unable to tear himself away from his fading portrait on cable news. What reason he gives for resigning I do not know. I just imagine that at some point Kellyanne and Spicey will tell us, "Trump was never the president. That is a fact. Period." Then we all move on to the next stage of our insanity.