Maybe, but I'd like to think they'd know how that'd have been too obvious. They had always known the actual final shot of the show anyway (Jack's eye closing), and I don't really see how that itself could fit with the Island being purgatory, unless they had to die to move on from it or something.
Was the network that wanted to keep it going as well, I think the creators had planned for 5 seasons and the network for 8, so they ended up coming with the compromise for 6.