TCS joining date query

Hi all, I've received my offer letter from TCS and they have mentioned my joining date in it as Jun 23 and offer is valid upto 120 days. However I couldn't be able to join TCS on the mentioned date, tried talking to hr regarding the same and asked him to postpone it by one month. Hr said that joining date will automatically be postponed if i don't join on mentioned date and it'll keep on postponing until they manually withdraw my candidature. Will they revoke my offer after jun 23rd?