By leaving the EU, you mean?
Yes.
You seem under the impression that the British economy is the motor of the EU. It is not. It may turn out that the UK leaving the EU does the UK more harm than good. But I'm sure the PM knows this. Otherwise, why insist on free access to the euromarket?
I dont see why EU wouldnt survive. Maybe it would even become much more united and stronger politically.
The UK leaving in itself would not be a critical blow to the EU. But fault lines and cracks in the EU construct have been showing themselves all over the place in the last few years. The UK leaving might be a catalyst that finally breaks it. But I consider the possibility to be quite small.
I could see the core states of the EU becoming more united and stronger after such an event, but I think at the moment it would have to come at the price of ditching some of the current member states.