What is the Banker's biggest problem?

Chekhov's "The Bet" is an unusual story in many ways. For one thing, it is unusual because it deals mainly with the transformation of a man's character during solitary imprisonment for fifteen years--and yet it is not told from the prisoner's point of view but from that of the Banker, the man who is keeping him prisoner. Here is the opening:
It was a dark autumn night. The old banker was walking up and down his study and remembering how, fifteen years before, he had given a party one autumn evening.
Chekhov chose to tell his story this way because he needed to have a problem for dramatic purposes. The Lawyer has no pressing problem. He will be taken care of for fifteen years, and all he has to do is pass the time. In some ways he is in an enviable position. The Banker is providing him with comfortable accommodations, good food, even wine, books, and nearly anything else his prisoner could wish for. It would be a challenge, albeit an interesting challenge, to write that story from the Lawyer's point of view inside a lodge in the Banker's garden. But the Banker has a very real problem, and it keeps growing over the years. He is running out of money, and he is afraid he won't be able to pay off the bet if his prisoner really sticks it out for the full term.
And now the banker, walking to and fro, remembered all this, and asked himself: "What was the object of that bet? What is the good of that man's losing fifteen years of his life and my throwing away two million? Can it prove that the death penalty is better or worse than imprisonment for life? No, no. It was all nonsensical and meaningless. On my part it was the caprice of a pampered man, and on his part simple greed for money ..."
The story opens on the very night before the fifteen-year term will expire. The Banker's problem is now acute. The bet was for two million rubles. That was a relatively trivial sum fifteen years ago, but now it amounts to practically everything the Banker has left. If he pays off the bet tomorrow, he will be bankrupt. He will have to spend his old age as a pauper. But what is the alternative? He made the bet in front of a large assembly of important men. If he simply refuses to pay he will be disgraced. And, what is more, his prisoner is a lawyer! The Banker can be dragged to court and have a judgment lien placed on all his property, including a hold on all his liquid assets.
"Cursed bet!" muttered the old man, clutching his head in despair "Why didn't the man die? He is only forty now. He will take my last penny from me, he will marry, will enjoy life, will gamble on the Exchange; while I shall look at him with envy like a beggar, and hear from him every day the same sentence: 'I am indebted to you for the happiness of my life, let me help you!' No, it is too much! The one means of being saved from bankruptcy and disgrace is the death of that man!"
Chekhov was wise in only giving hints of what was going on inside the prisoner's mind during all those fifteen years. The Banker, as well as the reader, are taken completely by surprise when it turns out that the prisoner has experienced a complete spiritual transformation during his incarceration and no longer wants the money. The Banker gets to keep his last two million rubles, but he seems fated to have a wretched, meaningless existence for the remainder of his life. He has lost his nerve. He will be afraid to risk a penny of his remaining capital by lending or investing.
Chekhov created a chilling and memorable story when he made the artistic decision to remain in the Banker's point of view from beginning to end. The reader actually sees the folly of materialism which the prisoner repudiates in his departing letter. The Banker's lust for money nearly drove him to commit a dastardly murder and to contemplate pinning his crime on one of his servants, who would get sent to Siberia. The protagonist was saved from having to commit the crimes he was planning, but he knows in his heart he has become a cowardly villain, an ugly specimen of humanity.