What happens when a SDL, T-bill and G-sec matures?
When the T-bills mature, they are debited from the demat account by the government automatically. This is called the extinguishment of securities. The amount will be credited to the primary bank account linked with Zerodha within 15 days.
CDSL will send an SMS to the registered mobile number upon maturity. The transaction can also be viewed on the holdings statement. See How to download transaction cum holding statement?