In other words, How does the IC fabricator solder these thin wires between the die and the pads and guarantee that the soldering iron temp (300C for example) on the IC pads won't desolder them?
The bond wires are not soldered to the die. They are predominantly attached via a process called gold ball bonding. It uses gold bond wires, and welds them to a gold pad on the die using a combination of heat, pressure, and ultrasonic energy. Gold melts at a much higher temperature than any soldering process, making for a solid bond to the die.