When Article 50(3) is invoked there will be a two-year period in which the U.K will negotiate a new relationship with Europe. Until then the status quo continues to apply.
The effect of Brexit goes well beyond trade or immigration. EU legislation is heavily enshrined in UK law for decades. Any primary legislation enacted to incorporate EU law would remain in place unless and until it is expressly repealed.
However, EU law incorporated by secondary legislation would in all likelihood automatically disappear as soon as the UK Parliament repeals the European Communities Act, unless such repeal is with express savings.
We have produced a table providing an overview on the alterative models available to the UK which briefly summarises the possible/likely effect each would have.