Is this intended behavior? Seems insane if so.

Yes, Not solving the maze should result in a death of the player. That is the intended function of the reward.

Is that common behavior for this mod? There seems to be a balance issue.

Does it still command-kill the player if they teleport out? Is it aware of Hardcore mode? Does it respect the Focus Sash?

Would it be possibe to teleport the player into a wall instead of something this extreme and unexpected?

There's a balay issue simply because you can't balance a mod like this for every scenario.

No the mod does not command kill, but does deliver the same effect as command kill for some rewards to make them fair. If you teleport out it still will kill you if you don't complete the maze. No the mod does not know hard core mode, but if you are you should either be pruning the mods rewards as not all of them are good for hard core mode or simply not be using the mod. No idea what the focus sash is, but I can only balance the mod for vanilla play as that's all that is in my control.

Read this if you want to know more about this stuff: http://blog.theprogrammingturkey.com/2016/11/10/why-making-rewards-for-chance-cubes-is-not-easy/