two way mirror of sirius

[kashelkar]

No: HPFGUIDX 92818

Kashelkar writes:

At the end of Christmas vacations, Sirius hands Harry a badly wrapped 
package.  It contains a two-way mirror, Sirius having the other one.  
So if Harry talked into it, Sirius would be able to see & listen him 
and vice versa.  How come Sirius never uses it himself??  When Harry 
broke into Umbridge's fire to discuss with Sirius the worst memory of 
Snape, why Sirius didn't ask him not to use such dangerous method to 
contact him again, and rather use the mirror given by him???  
Certainly, if Harry hadn't forgotton about this mirror, He'd be able 
to check that Sirius is safe after his vision and Sirius needn't die 
at all.  Also, if it was never to be used why did JKR introduce this 
item in the story at all???