I don't believe that immigration will change whatever the result is.
If we stay, nothing will change. New countries will join the EU and they'll be able to come and go freely, as will we.
If we leave, I think we'll end up having some kind of reciprocal movement for EU nationals as Switzerland and Norway do, which means that any countries joining the EU in the future will also have freedom of movement to the UK, so no difference.
For non EU immigration, the fact that we belong to the EU means nothing currently. People either meet the requirements of the Rules or they don't. I don't believe that will change if we leave. We'll still have students, tourists, workers, spouses etc.
For illegal immigration (including asylum seekers, economic migrants, overstayers etc) absolutely nothing will change whether we stay or leave. People will continue to overstay visas, use false passports or lie to get visas in the first place and asylum seekers in Europe aren't suddenly going to halt their journeys because we've left some central organisation that is likely to mean very little to them in their day to day life.
Unless we start abolishing more than our EU membership, we'll still be signatories to the 1951 Refugee Convention and the European Convention on Human Rights, so anyone who has committed a crime in the UK and can't be deported because it will be a breach of their Human Rights to return them, will still be going nowhere. All this guff about closing the borders is a load of rubbish. It's physically impossible.
It terrifies me that some people genuinely don't see how much Britain depends on immigration, or any of the wonderful things that immigrants to this nation have brought with them, and instead seem to believe that an exit vote means that all the 'forriners' are just going to disappear.