OK, this is pure conjecture on my part but...
The EU seems to be a in a hell of a mess and, much as I would like to, I can't see it getting any better. I'd go as far as to say the next couple of years will possibly / probably see enormous problems, especially if the hugely unstable Turkey is allowed in (yet they seem to be being fast-tracked, for no good reason that I can see!)
Wouldn't a hugely rich economy like the UK (fifth largest in the world!) become MORE attractive to potential investors if shit goes south in the EU and we had already beaten the rush and left early? Boeing just announced that they're setting up European investment in the UK. These people aren't thick, they've got their $$$s in mind. Surely others will follow? I do understand that there might be an initial wobble, the pound going weak against the Euro etc in retaliation for us having the nerve to leave, but it might be better in the long run? Especially if the multitude of problems in the EU get escalated, further and further...
As I said, it's my own silly conjecture, I don't claim to be an expert in politics or economics, but no more so than the predictions that others are making about what will happen to the UK in the face of something that has NEVER happened before.
Feel free to shoot me down on this.