As stated, Hillary cannot become president no matter how many people were impeached. Wouldn't an easier and far more likely example be "if a democrat wins the election next year"?
A lot of the executive orders he did that don't require congressional approval, like placement of tariffs on China, could be undone with the stroke of a pen. Just like Trump undid a lot of Obama's executive orders, but wasn't able to undo Obamacare since it required congress to vote on it. Likewise if a democrat wanted to undo Trump's tax cuts they'd have to get congress to approve it, since that was not / cannot be done via executive order.