I'm assuming you mean that you have an employment contract with a company that has been acquired by another company.
Early on the acquiring organization will assess staffing needs and whether your services are still needed. Be alert that at some point the old company will officially be dissolved, thus you will no longer be an employee of that organization. HR should let you know officially that you are now an employee of the new organization and thus bound by its policies. Whether you are owed payment depends on the language of your contract and the policies of your company. Don't count on much of a severance payout unless you're a long-term employee with a backlog of unused vacation.