Welcome to Just Answer , The PAS belt also dries the alternator and air con compressor so removing the belt is not an option.

You may be able to top up the pump and clamp off the down pipe but I think pump damage is the least of your worries , 9/10 PAS fluid loss on the Vectra B is internally in the rack as usually its the pinion end seals that go and fill up the bellows so there is only so much fluid you can put in before they burst , of course it may be on of the external pipes leaking but as i say 9/10 it is the rack.

Driving like this is not much fun , it happened to one of my Vectras , its OK on the straight but slow moving is a bit of a mare , it could also have implications with your insurance and the boys in blue .

I hope this helps , best regards XXXXX XXXXX

There are 2 pipes to the pump 1 feed (gravity) 1 return slight pressure but thinking about it again there may be more fluid returning than leaving so it will get messy so best not try this .

The grinding noise is a hydraulic fluid noise and not metal to metal so the pump will not suffer too much.

You should really put the car off the road as you have a steering fault but try topping it up and see how it goes.

Driving without PAS is very heavy and not recommended its your choice.

regards XXXXX XXXXX