PbP is unfortunately a very hit or miss situation. You're looking at somewhere around a 10% completion rate for games (if that). Some games go along great and suddenly something happens. Csjarrat and I were in a game where one of the PCs challenged the GM and the GM straight up disappeared. I was in a ton of D&D games on the Wizards boards back in the 2000s and only one of them went to "completion" (and it took about 4 years).
Shadowrun tends to be pretty similar. I've been in 4 games so far. One I made a solitary post before the GM disappeared, one that got just past the meeting with Johnson before the GM stopped posting, one that got pretty far into the first mission before the GM disappeared, and the final one which is still on-going and is nearing the completion of the first run. In all of the games, we had players disappear. It happens, but what killed the games was the GM disappearing. If you want to keep up with it, you can probably find players to replace those that abandoned the game. In any case, check with the PCs that are still around, modify the run if necessary, and stick with it, they'll stick with you. Additionally, once there is some posting and gameplay, other interested players can see your style and may want to sign up.