Question

If magnetic monopoles would have existed how would the gauss law of magnetism be modified

Answer 1

then gauss law will become integration of B.dS = Qm/mu
where Qm = charge of magnetic monopole
and mu = permeability of free space

Answer 2

Hey !!

Gauss law of magnetism describes that divergence of magnetic field will be zero while divergence of electric field is not zero which shows the non existence of magnetic monopole. As per Gauss law of magnetism

                                  ∫B.ds = 0

If monopole exists, then the right side will be equal to the monopole which is multiplied by μ₀.

Good luck !!