Meanwhile back to the question:
No, they should not be granted amnesty. When this tragedy happened I made a guess that the authorities will never know how many people perished. That is simply because they have no idea how many people (or which people) live in such establishments. Many original tenants in such places sub-let the property (often to a far greater number of people than it was designed for) whilst drawing considerable assistance to pay their rent. Many of the illegal sub-tenants go further and rent space to sub-sub-tenants. Many more simply squat with others. It would not surprise me if, in the 120 flats, there were around six or seven hundred people resident.
The tragedy is terrible and nobody deserves such a fate. But there is simply insufficient accommodation in central London for such numbers of people and quite why the authorities insist on spending huge sums to provide housing which is clearly unsuitable is a little puzzling. I cannot afford to live in Kensington (even the rough end) so I see no reason why people less well off than me should be provided with heavily subsidised accommodation in such an area.
If my house burnt down I would be told to scour the ashes for my insurance policy, contact my insurers and get on with it. Quite what makes these people different befuddles me.