Understanding semiconductor failure mode
The TNY264 is a highly (electrically) stressed IC which sees mains voltage, probably part of a low wattage auxiliary power supply that is always present waiting for the soft power switch to be pressed. 

The typical root cause would be a mains transient causing the internal MOSFET to avalanche, resulting in massive current and blowing the wires off the chip, cracking the package etc. Once the MOSFET fails short, the fusible resistor is next, protecting the transformer and wiring. 

Since it worked for a long time you may not be too concerned, but if there is something new you've added to the electrical load nearby (perhaps a refrigerator) you could consider adding a surge absorbing device. There is no reason why this would not happen again.