Well, I would like my Architects to keep their creative gamemode. It's not that nice to fall down and die when you log in again..

I had this problem, I used a repeating command in the form of a function to change anyone in survival to adventure. That way I can still use creative, but regular players are kept in adventure mode

In a vanilla setup players keep their gamemode. So if yours don't then there's probably a plugin which is causing this behavior. Find the plugin and re-configure.

To my knowledge (from mind anyway) both GriefPrevention and WorldGuard support this feature, and those are quite commonly used.