They will survive the holocaust. They will be the most evolved animal after we all die.
Tardigrades are polyextremophiles and are able to survive in extreme environments that would kill almost any other animal. Some can survive temperatures of -273°C, close toabsolute zero, temperatures as high as 151 °C (303 °F), 1,000 times more radiation than other animals such as humans, almost a decade without water, and even the vacuum of space. In September 2007, tardigrades were taken into low Earth orbit on the FOTON-M3 mission and for 10 days were exposed to the vacuum of space. After they were returned to Earth, it was discovered that many of them survived and laid eggs that hatched normally, making these the only animals shown to be able to survive the vacuum of space.