How to cope with changes in the plot?

When I first outlined the plot of my novel, I wrote:

"Usame needs the cheap labor that comes with Xicomean illegal immigrants, and some of Xicome's crops—like coffee and sugar--, and Xicome needs the products made in Usame. There is an interdependence, although Usame tends to underestimate this intertwined relationship."

But in the last 2 posts, I wrote a different story, where the Usame's council was made up of old landowners who planted coffee.

I will have to rewrite the beginning of the story to follow my original plot.

What do experienced writers do in this case? Do they go on writing what comes up naturally or do they rewrite to follow again the course of the original plot?

If anyone knows, please tell me.