What happens to the game if processes crash?
Most of the game processes will disconnect the subset of the users handled by that process if they crash. The game as a whole will only go down if the World Server crashes.
How do the game servers communicate to the clients?
The communication is currently done across TCP connections. Support for UDP connections is an ongoing process.
How many maximum concurrent players are supported in the same world?
The maximum concurrent players in the same world is only limited by your server cluster size. You can add more servers to support more users. At some point there would be a bandwidth limitation in your transport layer (or, less likely, pipe to the internet) but where this occurs is based entirely on your game design and implementation. For example, some game designs require very high-frequency player movement updates and others do not.
In general, concurrent players in a world is not a problem. However, you do have to be concerned over how many concurrent players are in a given geographically region of the world (what we call an "Area"). But, again, the limitations here are driven primarily by your game design and the implementation (by your team) of that design. Smart design and good implementation can yield hundreds and hundreds, or thousands. Once we know more about the requirements of your game design, we could provide more information.
Do HSL classes have the equivalent of a constructor?
For more info, see: Constructors/Destructors
Why, when I try to log in, do I get an error called "FSERROR_CONNECTIONFAILED"?
The error "FSERROR_CONNECTIONFAILED" indicates that HeroBlade attempted to open a connection and it did not succeed. Meaning that either the world is down, which is rarely the case, or there is a networking issue between your computer and ours.