The common travel area does pre-date the EU, but everything in terms of travel rights has to date been based on UK and Ireland being on the same page regarding the EU - both out or both in. So it's pretty likely that Brexit will create some changes/problems, whatever the UK decides to do 
I think physical border controls at the NI border would be an absolute last resort (mostly cos it would be so expensive, I can't see the UK govt paying for it), but we might see the island of Britain being ringfenced for border control instead. As in everyone will have to go through passport control when travelling from NI to rest of Britain, same as if you were travelling from Ireland, France, or anywhere in the EU. A political nightmare, but still easier than reimposing a land border...
The rights of Irish and British citizens to live, work, vote, etc. in both countries has a good chance of staying as currently arranged, but no guarantees. It might be restricted to NI alone, which is good for people who live on one side of the border and work on the other, but not so good for the Irish expats in England, Scotland, and Wales. With this Tory govt, who have little knowledge and even less interest in Ireland and NI, anything is possible.
I recommend 