IMO the worst case scenario is not that it stays in alpha/beta forever, but that they 'release' Star Citizen 1.0 and it's still broken and lacking meaningful gameplay.
That's actually highly likely. Best case scenario is that most of it works in over 50% of your playtime with high class hardware and internet connection and a couple of star systems present (say 3-4).
And then they move on to another game.
I doubt that. The unfinished potential of SC (which is basically on MMO) will provide them with enough things to build, moneytize and exploit for at least 10 years going on from point of release.
With early access games a lot of times release marks the death of the game, because everyone was sticking with it on the hopes that the devs would finally turn it into their dream game, but the final release rarely fills that role. Fortunately, it doesn't seem like CIG feel any pressure to drop a 1.0 release anytime soon
They have already a huge fanbase that is enjoying SC right now as aweful as it is atm. Plus they built a complete infrastructure for moneytisation, community and cross-selling.
The finished game would be basically what Second Life hoped to achieve just in space. And it will cover a huge base of players interests (sim, egoshooter, adventure, exploring, sci-fi, trading, socializing). It would become basically a second life for people to live in if they want together with everything to sell you that you could buy in reallife. And with a connection to real money the opportunities to earn money for them are huuuuge. Even if it's free to play after you bought the game. There are always cosmetics/fashion/decoration, buying ingame money (even if the game isn't designed to exploit that). Or outside of game subscriptions for extra content to enjoy like the e-zine Jump point right now which even gives you some goodies for the game (3d-objects for decoration). Even the ingame money wouldn't be such an exploit because skill in the game still matters, at least on ground level with egoshooter mechanics. Even contacts to other players will matter.
Right now to keep the game going with funding for some additonal years they have to optimize performance, squash out bugs for the core gameplay, bring persistancy into the world, make npcs interactable and provide let's say 3 fleshed out star-systems for people to play in. After that they can basically run the game for another decade in that unfinished state by simple expanding the game and let players buy game stuff.
To make a long story short I don't think people would buy a second game from them if they abandon Star Citizen and Star Citizen has too much work left and opportunities to earn money to abandon as long as the technical side doesn't reach the critical mass when everything breaks down into pieces.
