Student Teaching Minetest Modding in school as club
You seem to be focused on game development, which is probably the right thing to do since at least some of your student colleagues will also be interested. But there are other possibilities to keep in mind, such as some simple information system that your school might use. Teachers might be able to give you ideas about that. 

Since you want the club to continue after you leave, I'll suggest two things. You should probably try to develop one student to take your place and spend more time with him/her to foster a leadership role. 

More important, I think, is to pick the right project for your group. If you aim for a large result that can be built in parts and where each added part adds visible value (punch) then you might have something sustainable. You don't want a small project (or set of projects) since continuation means finding more projects. You don't want a project that isn't useful/cool/exciting along the way (but only at the end), since you don't get any psychological reward as you go. Pick a project that is large enough so that it can't be "finished" in the time available. It will then be an inducement to continue in the future. 

I'd also suggest that you don't try to lecture, but rather form an Agile Software Development programming team, using some of the practices of Extreme Programming. See Activities and Practices at the last link. There are other possibilities but XP is fairly easy to follow. Use short iterations and small stories. But make sure that each story adds gaming-value: something that will actually affect the play of the game. 

The above will also favor collaboration, which is a useful skill. Don't worry about absent students. Work with what you have. If the thing is interesting enough people will want to participate. But it has to be interesting both in its own right and also in the day-to-day activities. 

I would also suggest, pretty strongly, that, rather than laying out a curriculum for this, that you explore topics on a need-to-know, just-in-time basis. Making it like a regular course might not be as appealing to others as just keeping it like a club.  

Don't exclude newbies, but incorporate them, and their enthusiasm, into the project and enable it with Pair Programming, starting them out as Navigator with one of you "old timers." 

Good luck with this, and in your future.