You've already moved it, and it might have damaged the existing paste.
IMO, it would be safer to remove it, clean it, and re-apply the paste.
Why take a chance...?
It is critical that the Northbridge chipset is cooled properly for long term operation.
The heatsink must be seated properly, or you might experience "inexplicable" problems: crashes, freezing, or it might even die.
It is your decision, but I would re-seat it.