Those addon cards will be active till their expiry date, or till the primary card is active, or till you use the addon cards atleast once every 365 days.
If the bank close the addon cards, you are free to reapply again, provided that you will have to do vkyc again for each new addon cards.
This is a standard process for every bank. Some rules might differ from bank to bank. A quick free tollfree call to customer support will answer all your queries.