If the owner does not bring the loan current or sell the property as a short sale, it will be foreclosed on by the bank holding the loan. At that point you could attempt to purchase the property at the trustee sale (auction) which would require all cash.
If you buy a house that is listed as a short sale or bank owned, you may typically finance the purchase depending on the condition of the property. Please contact me if you would like a more in depth explanation.
There are hundreds of other possibilities.