If it is a Honda nothing much, on rest of the bikes engine can seize.
But one thing 4 sure would happen, ur engine wud get weak too much B4 time. Little scratches on the piston and cylinder walls ,that are microscopis and cant b viewed by naked eye, multiply and tranfer damage to other parts. reducing the power of engine and its efficiency..
Running on an ideal RPM smoothens thoose parts and polishes them.