You know, this isn't that kind of thing that makes people happy: just having a demo (a long demo, ok, but still a demo) doesn't make us want to buy the entire game but the opposite! Really, this just isn't fun.
I really love Idle Games, really, A LOT! BUT, and I say BUT, you MUST had an autosave or a save button! I suggest that evry island or 5 creatures an auto save is activated. Otherwise all the work is gone by accidentaly pressing that damn x red button!
A game like that already exists: it's called monster castle or something like that. It should also aailable here on Kongregate. They have different graphics but the game concept is just the very same.