Although Trump supporters would certainly be very angry if he was impeached, I don’t see that they would be very likely to stop selling their crops etc. They need the money. And there are plenty of foreign alternative sources of food, though more expensive.
I think it’s more likely they’ll start voting extremely conservative, possibly splitting off to a third party. Further, I think it’s very likely that Trump would start and lead that third party. The remaining Republicans will move toward the center, possibly eventually becoming a truly moderate party.
Splitting the Republican party like that would hand more power to the Dems in the short term. But they would likely use that opportunity to move to the left. Over time, moderate Dems would start moving to the newly moderate Republican party. It’s easy to imagine a realistic scenario where, 20 years out, a newly moderate Republican party is somewhat dominant while the far left and far right are represented by Dems and Trumpians.