You are not supposed to pay off the loan, do the main quest.
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Tried to, but most of my runs (B4 NEW ver 5.2B) were going past D28-----so *STILL* paying MIN 4k gold to greedy bank.
In some cases (mentioned elsewhere) it's b/c was short on Guild Points----even in some cases where didn't miss *ANY* Quests! [because some Quests simply didn't pay enough Guild Points!) Quests need to *AVERAGE* 167 Guild points EACH---or you won't have enough points before D28.
Oh, another Quest that's killed me early----Monster Hunt----UNDEAD. (EXTREMELY difficult 1st 14 days!)