Well there are some problems with your model. I can't quite justify its Ceteris Paribus either.
There's an instability in your logic there. Spending goes down to $7,650 so there's enough rationale to fire a second person, dropping it to ~$6,900. Then everyone still working gets their hourly time reduced, further reducing their salaries, which reduces the time they work which reduces their salaries. etc.
The problem is its important to consider the bank as part of the economy, otherwise both the savings and interest payments are reducing the economy by ~10% at every iteration.
Yes, it is part of the economy, but some of the money will not reach the consumer or may reach him after a series of iterations and transactions that slow down the flow of money until it reaches consumer, which is the equivalent of liquidity reduction for the economy.
Such credit money may become dividends paid to shareholders (rich people may not spend the money in your country, and if they do, they will not pay consumers directly, but he would pay people who will pay employees after some time).
Such credit might be invested somewhere, it may be used in multiple ways that slow down flow of money.
So what I did here is a simplification of the reduction of liquidity, caused by banks.
Another stable solution is that production and prices remain at a certain constant level and excess goods pile up in the stores and excess money piles up in the bank(production constant, consumption is not). If savings is continued and both prices and salaries are reduced (production and consumption constant), this is not stable as a larger amount of the money supply gets banked.
In theory it sounds good, but keeping inventory means financial cost of opportunity, and goods could get deteriorated, and also you have costs for just keeping them (warehouse costs, handling costs, refrigeration, heating, air conditioning, etc). Somebody will have to pay for this.
So the money in the bank has to go somewhere, and banks don't earn interest magically, they have to make loans. Either the company could take a loan and invest it directly into meeting its short term production costs (or changing some aspect about its production, we'll ignore it as it violates Ceteris Paribus) or an unemployed worker could take a loan to meet his consumption requirements. If all workers are equal it would be possible to rotate the unemployed worker and nobody's debt or bank account would pile up.
Yes, they make loans. I worked for a bank. Bank services are always designed to make you lose. It is like a casino. With their financial games they always win with every move.
If you put their money there, they will invest it and they will gain higher profitability with investments than the interest that is paid to you. Some banks pay you an interest that is lower than the sum of devaluation and inflation, so indeed your money is losing value and they make money with your gap.
With credit it works this way. Someone puts his savings in your bank, lets say you pay 1% interest rate. You lend money with a 3% interest rate, and then you won 2% out of nothing. Some lending comissions, legal fees and some extra costs are paid by customer. That 2%+ is your profit, while your administrative costs are reduced as you increase the scale of the operation.
Another trick is to design products that collect interests over interests. For example, you have a credit card in your bank. Commerce pay 7% of their revenue to you for the sole fact of having customers using your card in their transactions. It is evidently being paid by the customer.
As customer find a very expensive good, bank decided to create a certain type of "loan" using credit card, so you buy the good, and the payments of that loan (which already has interests) is charged to your credit card. If you get delayed in paying your credit card, it will collect interest on the payment that already include interests.
I learned something. Banks never lose. You do. They design things so you lose, and you can't possibly win.
Banks are known for taking money out of economy, like a leech, and as money does not turn so fast into salaries, they reduce liquidity.
