when the diazotisation is done above the temperature of 272-273 , what happens to the compound?

In the case of reactions forming diazonium salts, there has been a common rule of thumb that they must be kept somewhere between 0 - 5°C:

In aqueous solution diazonium salts are unstable at temperatures above 5 °C

At temperatures above 5 °C, diazonium salts (in aqueous solution) have been known to decompose, often explosively, to liberate nitrogen gas, temperatures too low however can cause crystallisation, which causes issues later on (diazonium salts should never be dried upon isolation - they explode).

Although people often keep to this rule of thumb, theres no real body of evidence for its generality (i.e. different diazonium species will have vastly different decomposition temperatures).