| I've seen cars in a much worse state than yours repaired and returned to the road, so considering your's is less than 3 years old and still worth a fair bit it is highly unlikely it will be written-off.
As cco7ers has already said, it will be like new when you get it back, as it will have a virtual full respray.
As for MINI Insurance, they are actually just a trading name of UK Insurance, one of the biggest insurers in the UK, so you've nothing to worry about in terms of them doing a good job (they will only use a BMW Approved Bodyshop) and honouring their side of the agreement in providing you with a replacement car. Just don't expect it to be a MINI, as they source the cars through Enterprise.
It's horrible when stuff like this happens, but put it behind you now and don't let it bother you. | 
