This might be a little far fetched but what about another option or even this option incorporated into any of the other two options suggested already...
It has been suggested before that when a new game world opens, there could be already established airlines (run by the simulation) operating on routes before said world has even started. This idea was supposedly an option to limit how quickly/aggressively player controlled airlines could expand so that they didn't dominate everything and everyone in just a matter of a few game years.
Now my suggestion would be that at the very beginning of when you go through the process of picking your airline name and operating base, why not have an option where the player can choose whether or not he wants to take over one of these (simulation) airlines or start his own from scratch?
I think for the more experienced players, they would rather start their own as this would add an extra dimension to the game because it provides them with yet another 'challenge' to overcome by trying to compete with already established airlines. This would add more excitement to these players and might give them reason to keep going in the game rather than bankrupting because it got mudane or boring for them.
As for the less experienced players or even beginners, they would be more inclined to choose an already established airline 'to see how it can be done'. They can look around these airlines and get an idea of how things run in the game, giving them useful hints and tips on what they should actually be doing. This could in some way be linked in with the tutorial idea.
Or if they really want a lesson then they would choose to start from scatch also.
This could also be incorporated into option 1 whereby when the CEO decides he's had enough and quits, the airline is then run by the simulation again (whether it be from a player who started from scratch or if it was a previously run simulation airline). Even if a less experienced (in the beginning) thinks he/she has now got the hang of things after a while, they might think of leaving but instead of just leaving the game altoghter they might decide to start their own airline from scratch, now knowing how to run an airline without bankrupting several times over like they do at the moment. So in a sense, this could be a sort of tutorial for them.
This could also tie in with the 'CEO wealth' structure that has already been suggested in this thread so you could actually create quite a few possiblities in progessing forward in the development of this great game.
I think with these ideas, it would give players in the longer game worlds more longevity with their airlines rather than bankrupting because they're bored.
Anyway, i did say it might be a little too far fetched but it just popped into my head while i was reading through this thread and i thought i might aswell share this with you and see what people may think.