Say if a blackhole passes very close by a neutron star at high speed fly-by and eats half of the neutron star. What happens to the other half? Does it blow up in size as the electroweak force pushes away the protons from the electrons? Would it create all the elements in the periodic table and throw them in all directions?
I cannot really say much about the energetics of the collision, but I think there is no problem at all in a typical neutron star losing half its mass and remaining a neutron star.
The minimum mass for a stable neutron star is about 0.2 solar masses. An object a bit more massive would be much bigger than the usual 10km radius, would have an equation of state dominated by neutron degeneracy pressure (as opposed to the strong nuclear repulsion between closely packed neutrons) and would not feature any exotic matter at its core. The crust region would be a bigger fraction of the star and of its mass.