A novel with multiple beginnings, middles, and ends is a multi year project (I've been working on Scarlet Moon for about a little over 4 years now). No need to go that crazy for your first game.
Keep it short, and contained. Then, if the characters and settings take off, feel free to make it longer. If not, move on to bigger and better things. Or more small and better things. Whatever. Some people get more satisfying out of creating small, complete games and moving on to the next one. Others get more satisfaction out of spending a long time creating and developing bigger, more complex games.
For a few games you can take a look at, here's one that I wrote in about a week, writing for a couple of hours each day, for a game jam a few years ago:
http://www.spankingrpgs.com/wp-conte...-Shackles.html
You can also look at Get to Work from Pirate Life:
https://animeotk.com/forum/showthrea...ext-37167.html
Both games are fairly small, but have very different structures. My game is fairly vertical: you have lots of decision points, but the game doesn't give you many options, and many of the options are either dead ends, or lead to the same result.
Meanwhile, Get to Work is more horizontal. The player makes fewer decisions, but more options are provided at each decision, and each choice is more fleshed out, and leads to more different content.
