I don't think that's really a fair criticism, of course they don't know yet - there will probably be at least hundreds of people involved in years of talks and negotiations to actually put together a complete, concrete, plan.
You really can't expect the politicians to magic something like this up, there isn't even a broad consensus about whether to join the EEA or not, so anything more specific would be completely pointless at this stage.
So if Leave win, we get years of turmoil and uncertainty, both great things for a country's economy, and may end up either standing alone with the borders closed, or all but in the EU with us in their trade zone, paying them millions a week and co-opted into schengen with even less border control like the Scandinavian countries. It's less a remain / leave vote, more a stability / chaos vote.