Gladwin has been recalled by Queen's Park Rangers while El-Abd, Thomas and Thompson have gone back to Bristol City, Birmingham City and Norwich City respectively at the expiration of their loan agreements.
Swindon Town can also confirm that Henrik Ojamaa has left the club after agreeing a mutual termination of his contract.
The Estonian international signed for Town in September and made 11 appearances.
The club would like to thank all five players for their service to the football club during their time in Wiltshire and wish them all the best for the future.