They killed off a female lead in the first episode last season and it has been repeatedly said that this season will be more light hearted than last season because it was so dark. Starting off season 4 exactly like season 3 would be daft and Stephen Amell said himself "were trying a lot of new stuff this season" ! It just doesn't add up to start season 4 with the death of Felicity.. Obviously something brings Ollie back to his city but i don't think this is why.. Possibly finding out about his child would be reason enough to return and taking up the mantel of green arrow and protecting his city could be, partly, Oliver's way of building a safer city for his child??