In my experience that's pretty much what ALWAYS happens :P, either because the others don't have enough time or I'm the one that doesn't have the time the others need.
Finding a group of people with equal passion and dedication is the hardest part of creating a team.
Only thing I can think of to tell you is that if you really like the game, keep working on it, use pre-made assets for everything.
When you get it done maybe the others will gain enthusiasm again and work on it. If not then tell them that you'll proceed with other people and ship the game