law: Indian Contract Act, 1872 
  6. Revocation how made
  A proposal is revoked-
  (1) by the communication of notice of revocation by the proposer
  
  to the other party;
  (2) by the lapse of the time prescribed in such proposal for its
  
  acceptance, or, if no time is so prescribed, by the lapse of a reasonable time,
  
  without communication of the acceptance;
  (3) by the failure of the acceptor to fulfill a condition
  
  precedent to acceptance; or
  (4) by the death or insanity of the proposer, if the fact of the
  
  death or insanity comes to the knowledge of the acceptor before acceptance.