It most likely has to be paid to you, but the absence of clear written terms means that the employer has room to try to argue that it should not. When there are no clear written terms, the court (if one side or the other sues, such as if you sued to get the money) will try to figure out what the parties most likely and reasonably intended. If you had a guaranteed bonuus for 2018, then the most likely reading or interpretation is that you earned the bonus by staying through Dec. 31, 2018 and therefore you are entitled to it, even if you leave prior to it being paid.But if there are emails or any other messages or policy statements from the employer showing that the intent is that you have to be there when the bonus is paid to receive it, or they can show that in the past, people who left prior to payment did not get their bonus (showing that the company policy is that you have to be there at time of payment to get the bonus), they may be able to successfully argue you are not entitled to it, since those facts would be used to establish what the policy and intention was.