Yes, the cost to unlearn skills doubles each time. I assume the gold vanishes; if there was a way to trade or something to get any gold back that would defeat the purpose of doubling the cost.
Gold will run out eventually. I didn't make any effort to extract gold from all the merchants each time I leveled, but did collect and sell loot. I reskilled twice, raised the cap for skills I didn't end up maxing, and had almost enough gold that I could have reskilled twice more (a bit of malachite ore farming could have could have topped off my gold). If you check merchants each time you level (or from the fjords onwards, when they can have a decent amount) and don't waste too much gold, I'd guess 5 or maybe even 6 reskills could be possible.
Once you report back to Louis of the location for the bandits' camp, none of the quests inside can be gotten if you don't have them, or completed if you do. You can still enter the Temple of Doom (and defeat Jagon), but when you get to the camp there will be some seekers there ready to rush in and wipe out the bandits, who will all be hosile when you enter.
I assume the weapons on the table would still be there, but I picked them up when I first entered. I figured I would need to reload after I tried that, but nobody seemed to have a problem with me killing them, so I kept the loot.
Martis can still be in the camp if you mindread him in jail, but don't turn in the quest. In that case when you accept the quest from Louis to break him out of jail, when you arrive through the tunnel, you will find a couple of bandits have beaten you there. You have a choice of either fighting them or letting them go (which will get you an invitation to drop by the camp). In this scenario there is no cave-in in the tunnel.
