There is no way to tell, for there is not such thing as a perfect conductor. Presumably, the magnetic field would be frozen at the configuration existing when the conductor was first created. In actual conductors, however, the conductivity value may be large, but always finite, and the the magnetic fields inside them diffuse at timescales proportional to this value.
For simplicity, let us assume a conductor with uniform conductivity and light propagation speed.
From charge conservation, we get $$\frac{\partial\rho }{\partial t} = - \nabla\cdot\mathbf{J}.$$
Since $\mathbf{J}=\sigma\mathbf{E}$, and $\nabla\cdot\mathbf E=4\pi\rho$, this leads to
$$\frac{\partial \rho}{\partial t}=-4\pi\sigma\rho,$$
so that the charge density relaxes at timescales inversely proportional to the conductivity (fast). As I've stated, but not yet proved, the magnetic field relaxes at much slower timescales, so it is safe to assume that the charge density is always equal to zero.
From Faraday's law
$$
\nabla \times \mathbf E =- \frac{\partial B}{\partial t}
$$
We see that the slowly varying magnetic field induces a slowly varying solenoidal electric field, so that $$\left|\frac{\partial \mathbf E}{\partial t}\right|\ll \sigma \mathbf E$$. Therefore, Ampere's law gives us
$$\nabla \times \mathbf B = \frac{1}{c}\left[4\pi\mathbf J+\frac{\partial \mathbf E}{\partial t}\right] = \frac{1}{c}\left[4\pi \sigma \mathbf E+\frac{\partial \mathbf E}{\partial t}\right] \approx \frac{4\pi \sigma }{c}\mathbf E, $$
or $$\nabla\times\nabla\times\mathbf{B}= -\frac{4\pi \sigma }{c} \frac{\partial \mathbf B}{\partial t}. $$
From the vector identity $$\nabla\times\nabla\times\mathbf{B} = \nabla(\nabla \cdot \mathbf{B}) - \nabla^2 \mathbf B $$ and Gauss's law for the magnetic field $\nabla \cdot \mathbf B = 0$, we get
$$
\nabla^2 \mathbf B = \frac{4\pi \sigma }{c} \frac{\partial \mathbf B}{\partial t},
$$
which is a diffusion equation for the magnetic field. In an initial configuration with spatial variation scale $L$ the characteristic relaxation time is $$\tau_D \sim \frac{4\pi \sigma }{c L^2}.$$ In the limit of a perfect conductor, $\tau_D$ would go to infinity. In realistic cases, it varies vastly. I quote from Jackson's "Classical Electrodynamics":
For a copper sphere of radius 1cm, the decay time of some initial $\mathbf B$ field inside is of the order of 5-10 miliseconds; for the molten iron core of the earth it is of the order of $10^5$ years.
When the medium is a fluid, or a plasma, the magnetic field undergoes induction as well as diffusion. The relative effects of the two processes are often characterized by the magnetic Reynolds number.
