The end of service gratuity is a UAE legal requirement which you have to get if you have been here more than a year. If you leave within 7 years you will get back the 5% of your salary you have paid into the provident fund as well but not the company contributions.
If you stay 7 years you will get all of the company contributions (12% of your basic salary) as well as your contributions (5%) as well as any growth. If that is less than the legally required end of service gratuity the company has to top it up. I can't imagine it would ever be less though.
Hope that makes it clear. In any event remember that the calculations are done on basic salary and do not include bonuses, flight pay, housing allowance, training pay or anything else.