What would happen to the concentrations of Pyruvate, NADH and intermembrane H+ if the ETC
stopped working?

Stay the Same, Increase, Decrease

Explanation:

Glycolysis produces pyruvate which is functioning normally if only the ETC (electron transport) stopped working because the ETC happens AFTER glycolysis, hence pyruvate is being produced and used at a normal rate (no change). NADH is produced in the cellular respiration stage PRIOR to the ETC so it is being created at a normal (or average) rate, however, it is not being used and split properly (meaning, not enough) in the ETC stage hence it's concentration increases. H+ decreases because it cannot be made if the prior step(s) were not complete.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.