If a molecule with 8 valence electrons bond with another molecule, then:
Question is wrong; an atom cannot share 8 valence electrons with another molecule
The question is wrong, because a molecule having 8 electrons in its outermost orbit, has an octet configuration. Molecules react with other molecules to attain octet configuration. So, a molecule which has already attained octet configuration does not react.
Conclusion: Molecules with 8 valence electrons does not react. They are inert in nature.