Your employer is not obligated to provide your 2018 W-2 until January 31, 2019.  Based on what you said, it would be nice if they did.  However, the IRS has not released the 2018 W-2 form yet.

Knowing that your employer may not be around, make sure to keep accurate records of the income you received as well as any tax withholding.  You can do this by making copies of the checks you received.  You could also ask your payroll department to provide a statement detailing the total income you were paid as well as how much tax was withheld.  This is actually pretty easy for them to do.

If you do not receive a W-2 next year, no worries.   TurboTax can help you generate a Substitute W-2.  Try to get your employer's EIN (Employer Identification Number) just in case.  You may need this next year.