If a company is delisted does not mean their shares are worthless or their value is zero, Its just mean they are not allowed to trade on exchange.

Suspension of a company from trading by exchange might be for several reasons but once the suspended company complies with all regulations suspension will be revoked and the shares will start trading again.

So to add up

1. First research and find out whether the company is permanently or temporarily delisted in NSE and BSE.
2. Check whether shares are listed in other regional stock exchanges.
3. Write a letter to company's compliance officer, that you are willing to dilute your shareholdings.
4. Look out for broker's advertisement in newspaper offering delisted share purchase, you can sell them for a discounted price.