I think that because it wasn't your fault the Corsa guy's insurance have to return yours to the condition it was in - it won't be written off. (Within reason obviously, if the chassis was badly bent etc thay must be able to leave it if it can't be repaired.)
If it had been your fault, your insurance may well have written it off, but I think you'll be fine.
The boot floor's designed to do that to protect the passenger compartment, it can be replaced and be as good as new. You ought to be able to choose who does the work too.
edit: Look into one of those accident management companies too, they take their money from the other party and can give you a like for like car while it gets repaired.
http://www.carcrash.co.uk/static/services-our_services.asp
That's just one, plenty on Google. Costs you nothing.