Insurance - likely Cat C write-off

[carefulplodder]

Hi, can anyone help me with an insurance question? Just heard that my (13 year old ford focus -ha ha) is likely to be a write-off as estimate is £1800 to repair. We were hit by an HGV who admitted liability and are claiming against their insurance. I guess this will be a cat C write-off. Its still very driveable (and in good condition for the age), the HGV just hit lots of panels whilst changing lane - just a glancing blow but lots of cosmetic damage. I might buy back from the insurer - If its a CAT C do I need to get an MOT and VIC if I want to drive it again immediately? At what point does it become a write-off (I've just got the garage report today and they are informing the insurer so I assume it becomes cat C when the insurer declares this i.e. I have a bit of time to organise a new car or hire car (which they will pay for) or new MOT and VIC?

I am really confused and yes I could phone my own insurer but I've already tried this and they were not clear either!

Thanks for any help