Ive been wanting to go for hajj for some time and i think this year it’ll be wajib on me as i’ll have enough money to go, but my sisters wedding is on Eid al Ghadir.
(When my sister went for hajj she returned on eid al ghadir). If that happens i won’t be able to attend the wedding.

So what should I do?

Since Hajj is wajeb on you to go, you must go. Do not delay it, as doing so is sinful. Also, know that many groups return by Eid al-Ghadeer. All the six times I went to the Hajj I was back home by Eid al-Ghadeer. So go with a group that will have you back in time for the wedding.