Before things started going downhill? I agree. Umm... A few thoughts, let me know if any strike your fancy or if you had something else in mind:
1. Robin returns home but doesn't go outlaw either: a. he stays quiet (which is unlikely, I know) b. he pulls some kind of Zorro/Night Watchman where he plays rich but secretly roams around fighting injustice c. it takes more than a day for him to turn from lord to outlaw
2. Something post engagement to Gisborne a. playing up the jealousy b. maybe Marian runs away rather than marry Guy
3. An AU ie Marian's father passed away and she's the Sheriff's ward with all the difficulties and restrictions that brings