Just to add a little (especially to @dmckee's comment to @Florin_Andrei's response):
A typical, isolated neutron star stably resists gravity with neutron degeneracy pressure. If instead it is accreting mass from a binary companion, it may grow beyond the Tolman-Oppenheimer-Volkoff Limit (just like the Schwarzschild limit for white-dwarfs, except for neutron stars), at which point it will inevitably succumb to gravity and collapse.
Neutron-star collapse is believed to almost always form a black-hole remnant; the exact details are unknown, but there are numerous quite successful models. What exactly it would look like is unclear, but the emission would be much less than the supernova of a typical massive star, or white dwarf. The observational signature would be entirely unlike a type Ia, and most likely unlike a type II as-well.