Hull City full-back East joined the Cobblers at the end of August and made 19 appearances for the League Two club.
Liverpool forward Mukendi made the move to Sixfields at the start of the season and the forward played in 13 matches, scoring the winning goal in a 2-1 Johnstone's Paint Trophy success over Colchester in October.
Defender Smith was brought in from Swindon towards the end of November as cover and did not feature for Aidy Boothroyd's side.
A statement on the club's official website said: "Northampton Town would like to thank the players and their clubs for their assistance and wish all of the players every success for the future."
Meanwhile, Northampton expect to sign experienced centre-half Clarke Carlisle on a permanent deal before the weekend.
The 33-year-old, whose second loan spell at Sixfields concluded with the league win over Aldershot on December 22, is a free agent after his six-month contract at York expired.