Wow where did they come from?
Some of the roots look lost but other do not. The black coloration could be from the soil that they were previously grown in. It seems like there might have been a rule in play that wherever they came from was not allowed to ship soil, so they tried to wash it off. Some of that may be old fine soil still clinging to the roots.
The white ones are definitely ok. The way to tell if the roots are dead is to squeeze them gently...if they are dead they will be mushy or hollow, not firm. If the tips have obviously been lost and there is a 'string' hanging out its dead.
You should proceed really carefully and take each plant and thoroughly inspect it root by root. Cut off all the obviously dead ones, you can train damaged ones up to where viable tissue starts. Leave obviously healthy ones alone.
The damage has been done, IMO there is not a lot you can do to cause more. The plants look like they were previously healthy....there is a chance of course they will recover...but they have been set back by this treatment and it will take time and rehabilitation.
After you have trimmed up everything back to only what is viable, I myself would put them all into damp sphagnum moss and let them try are re-root before planting them.
