Despite it being cancelled, plot developments had been made for Season 4 and this would have been the basic storyline of the season:
Episode 1: The gang bury Robin's body and accept Archer as their new leader
Episode 2: Tuck leaves to do more travelling
Episode 3: Much realizes Tuck is heading to trouble and leaves to warn him
Episode 4: Prince John comes back and Archer tries to make him compromise to not kill King Richard
Episode 5: Prince John escapes, and Blamire (who survived the castle explosion) finds Archer and the gang and ultimately kills Kate.
Episode 6: Tuck and Much return, as does King Richard. Much and Little John tell him everything.
Episode 7: Prince John brings an army to kill the 4 remaining outlaws, and Richard tries to settle it by having a personal fight between the King and Prince themselves
Episode 8: Prince John makes Blamire the new Sheriff and has him rebuild Nottingham Castle
Episode 9: Much is kidnapped in the castle's dungeons, and Prince John interrogates him about Archer's plans
Episode 10: Little John thinks Robin and Allan's ghosts are telling him something
Episode 11: Prince John realizes he is alone and tries to kill Richard and the gang himself
Episode 12: Prince John successfully kills King Richard
Episode 13: The gang are forced to surrender when they realize killing Prince John would put England in trouble. They almost give in their lives, but two old gang members return from the Holy Land (presumably Will and Djaq).
I think this should happen:
Episode 1: They try to bury Robin But they then realize he is still breathing they take him to the holy land to visit Djaq and Will where he is healed still alive.
Episode 2: Robin is fully better and goes to see the king and Marian's grave- it is empty- Robin looks for her body.
Episode 3: The King returns with Robin and what's left of his gang.
Episode 4 : John and Richards mother comes to sort them out.
Episode 5: Prince John's men all turn against him and they overthrow him.
Episode 6:Prince John is hung drawn and quartered.
Episode 7: Word gets out that Marian's body has been stolen.
Episode 8: Marian's sister arrives in Sherwood forest and tries to tell Robin that Marian didn't die but now does not remember anything about him or their marriage but before she gets the chance he sees a hooded figure (Marian) and is about to shoot but then he sees her face everyone stands down except Kate (who doesn't know Marian) Kate luckily misses.
Episode 9: Robin tries to make Marian remember.
Episode 10: Marian still does not remember anything and falls in love with an old friend of Robin's (from the holy land)
Episode 11: They try to make Marian remember Robin she doesn't remember meanwhile Archer starts to flirt with Marian.
Episode 12: Marian starts to remember things like Guy and her Dad and the sheriff and the Holy land
Episode 13:Archer and Marian are engaged Archer proposed to her in the same tree that Robin proposed to her.Robin finds out and tries to kill Archer
Then a season 5