My good friend loved this girl for years and she loved him back just as much. They did not engage in any haraam act and hardly ever met. They wanted to marry soon but Allah took her away. Now my friend is in really shook and he wants to know whether he'll have her in Jannah, if he pleads with Allah? And if he marries another girl because of nikah being a sunnah, can he still have the girl he loves in Jannah?
The description of Paradise in the Koran is:
41:31 We [angels] were your allies in worldly life and [are so] in the Hereafter. And you will have therein whatever your souls desire, and you will have therein whatever you request [or wish]
If your friend desires and asks for marriage to his love, it will happen because it is the promise of Allah.