Actually there is an easy solution for the "not-repaying-problem".
Make it so in order to borrow X amount of money you have to put something that values at the same as a guarantee, be it a house, equipment, or even the account.
So, let's say a lvl 100 knight wants to borrow 100,000 gold. Well, the character will have to drop as a guarantee items that are valued (by NPC) at that amount and a bit more, so for example he drops a Magic Plate Armor (90,000 gps) and Golden Legs (30,000 gps).
Now, once the bank marks these items, there could be a system that prevent this char from trading them, dropping them in the floor, or even from dropping it when dying (in order to avoid people from exploiting this in order to protect their whole eq with a Red Skull it could be done so if you die without blessings, AOL, or on a redskull while wearing these items you will get a huge exp penalty on death.
So if the lvl 100 dies while being a redskull and wearing the MPA and Golden Legs, he'd lose something like 30 levels, lowering its level from 100 to 70; also, the highest the lvl the higher the penalty, a lvl 1,000 could get a 200 level penalty.
Then, after the prescribed days passes, if the character doesn't have enough money in the bank, DP or Bp, the MPA and GL will be seized automatically.
It sounds complicated, but this is the only way I can think off that could be "fair" so it's not exploited, and there's is fear from not paying your debts (like in real life lol).