Once your contract period ends.
You have to read the contract to see if you have to compensate your employer financially,
if they paid for your relocation expenses and you leave within the specified time say two years,
you may need to pay back the relocation expenses.
For sure that you may not get a good reference from this employer for your future jobs.
If you leave without giving 4 weeks notice per contract,
they may or may not charge you from your pay for any expenses they incur,
your health care premium,
that they cannot stop suddenly.
They probably wont take you to court though,
as that could be expensive in legal expenses and time consuming.
I hope so this answer will help you a lot.