Eligibility for Gratuity
Strictly speaking, as per law, you are not eligible for gratuity. However, there are ways to prove that the business and the actual employer have not changed. This is referred to as piercing the corporate veil. You need to show that the actual entity is the same in both cases; the number of people, location, clients, and nature of the business have remained the same.
If you have this information, you can file a claim with your employer for gratuity. If he denies the claim, you can go to the commissioner and file an official complaint. If you can prove to the satisfaction required under the law, you will likely receive the gratuity.
If you cannot do this, you will obviously leave your job. Another question to consider is whether you really have the time and money to pursue this? Remember, it is not compulsory for the commissioner to rule in your favor. If the amount at stake is not very large, you may choose to skip it and move on.