ਵਾਹਿਗੁਰੂ ਜੀ ਕਾ ਖ਼ਾਲਸਾ ਵਾਹਿਗੁਰੂ ਜੀ ਕੀ ਫ਼ਤਹਿ
Can anyone tell what do we do with old kachehre no longer able to be worn anymore?
Do we do their Sanskar as we do with broken kanghe and kesh?

I think we can throw out old kashere. As they are mere cloth once not in use. Dastaars and vastar can be cut and reused for rags and wiping cloths. But kashere are generally thrown away and never reused.