Fast food restaurants would fail quickly. Taco Bell could pivot to more rice and bean dishes, but burger joints would collapse (no time to source new foods, develop new menus, run ads, etc.) Many fast casual places would follow. Sit down restaurants would be able to adapt their menus more quickly. The sudden decrease in restaurants and demand for meat alternatives would inflate restaurant prices.

Supermarkets would fair better. At first they would massively discount their meat, then just throw it away. Some job losses in meat departments. Some sharp price increases for common meat alternatives.

Industry would try to push the excess meat into other products, hide it down the list on processed food ingredients, turn it into pet food, etc.

Billions of animals would be killed (often inhumanly) then thrown away. At best they would be euthanized and buried. At worst, left abandoned in pens and buildings to starve and rot.

Farmers left with unoccupied grazing lands would turn to alternatives. Some planting row crops in areas where they are less productive and thus require more fertilizer and water. Some turning to exotic plants with potential to be invasive. Some property left abandoned and quickly colonized by a mix of native and invasive species.