The fact that it’s neither automatic nor instantaneous, even if Leave gets 51% of the vote, is actually good for the Leave side.
It means you can vote Leave as a protest, but without worrying too much that you’re making a horrible irreversible mistake. It will still be incremental change and will take years to effect.
I figure even ‘leave’ doesn’t accomplish much for several years. The tipping point will be when Muslims control parliament. They are not going to like those pesky EU rules that allow non-muslims to just move to Londonistan whenever they want.