The thousand or so Jedi in Coruscant alone could probably deal with the threat if it was found soon enough.

And then there are the billions of clone troopers that are just waiting in Kamino; plus the trillions of droids.

Even if Coruscant was overrun before they could muster their troops; that's as far as the Slivers could get. A good amount of stardestroyer-like ships can reduce a city-planet to rubble in short order.

Any attempt to leave through starship would be easily neutralized via other star ships or throwing the mass of clone troopers/droids at the isolated 'mini-hives' until they are all wiped out.