Let $S$ be a $K3$ surface and $H$ be an ample line bundle on it. Given a flat family of coherent sheaves on $S$ whose generic point is a $\mu_H$-stable vector bundle, what can I say about the non-generic points? Are they always $\mu_H$-semistable and torsion free? In other words, is the moduli space of $\mu_H$-semistable torsion free sheaves compact?

Let $S$ be a $K3$ surface and $H$ be an ample line bundle on it. Given a flat family of coherent sheaves on $S$ whose generic point is a $\mu_H$-stable vector bundle, what can I say about the non-generic points? Are they always $\mu_H$-semistable and torsion free? I think that this is equivalent to requiring the existence of a compactification of the moduli space of $\mu_H$-stable vector bundles with fixed Chern classes, whose boundary points are $\mu_H$-semistable torsion free sheaves.