From what I understand, he only agreed/signed for one season because he didn't want to get tied down into a role like he did with Star Wars especially if it was for something he didn't end up enjoying.
But IMO there's no way they put that post credit scene in, if they aren't extremely confident that Isaac will be back for the role and relatively soon.
I'd bet they(Marvel and Oscar) were probably waiting to see early reception of the series and then started negotiating a new deal for a season 2 during the series and if they decides not to run a 2nd season, they would have left the post credit scene out of it.
But IMO there's no way they put that post credit scene in, if they aren't extremely confident that Isaac will be back for the role and relatively soon.
I'd bet they(Marvel and Oscar) were probably waiting to see early reception of the series and then started negotiating a new deal for a season 2 during the series and if they decides not to run a 2nd season, they would have left the post credit scene out of it.