Dear Rashmi,
Probation is a crucial period in a new employee's career and all his latent potentials suited to the job as well as the work culture of the organization are objectively assessed by his employer during this phase. If he lags behind in fulfilling any such standards, the employer is at liberty either to extend his probation so as to give him a chance to rise up to the occasion or to simply discharge him as per the condition contained in the contract of employment. At the same time, the employer can be considerate to certain real life situations which are quite unforeseen in a person's life not withstanding his employment commitments. Sudden and serious illness of parents which demands filial devotion is one such contingency to which no son can be indifferent. But, though he was compelled to go on leave so immediately without formally applying for it, he could have informed it without waiting for the employer to ask for this unauthorised absence for timely communication is an important aspect of employment. At times, it is quite natural that freshers get perplexed in uncertain situations like this.
Therefore, as a HR, you may verify the bona fides of the reason shown by the employee and if it is true and he is an otherwise suitable candidate in his functional head's evaluation, recommend the extension of his probation period in stead of resorting to discharge simpliciter at this stage.