Is there anyone who knows what happens when you pay Gaelan the money? I mean you will probably get Imoen back, but what about quests like Trademeet and so on. Do you leave the map or something or what, because I havent paid Gaelan yet as Im afraid that I cannot complete the quests.

Do not be afraid Luske the force is with you.

The whole idea is that "YOU" have to make the decisions because if you have to consult the great oracle every time you have to make a decision then you will be forever consulting and never adventuring.

Good luck.

Irakzai the Dark.

Irazkai (fellow Aussie) is right. Part of the fun is making your own choice. But your question is valid so I will give you an answer if you wish...
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None of the side quests in the game are part of the critical path so you can complete them whenever you want. There is a period in the game that might prevent you from doing so but you'll know that when you get to it.