I have also pointed folks to the post on the Articulate Blog- I think it's a great starting point for most folks- esp. Articulate users (although the concepts can apply to many tools).

Here's where I see most folks getting in trouble- how many paths/options/levels in this "choose your own adventure" are to be included? When do I branch to remediation? Where do I send them back a step to retry?...

I find folks starting really struggle with this issue, and often find themselves creating a bit of a beast and several potential dead ends.
So, I offer simple advice.

Rule 1: Build in reasonable, and most common issues - 80% of issues track to 20% of the source- start here. Get that shortlist, select the most important to include. Don't build every possibility, but the ones that are common pain points with the organization.

Rule 2: Give them the resources they will have on the job. I often find that simulation developers can create simulations that in no way allow users to access resources (i.e. Help Systems, Policies and Proceedures) that they can access on-the-job. If it is expected that they would (or in the case of P&P- should) use these resources while going through a scenario, work to include them. However, recognize limitations (i.e. asking a peer for the answer- guides/mentors can be considered and used appropriately).

And, as a last suggestion: KISS. In managing the branches, I usually tell folks there are essentially 3 flavors- use the stoplight analogy:

Green- you are on track- keep going, providing feedback where appropriate
Yellow- you are off track, but it is a small issue, which can be corrected and get you on track- provide feedback as appropriate, and allow things to continue (if appropriate have them reperform a step)
Red- "abort"- this is the dead-end where there is a core violation of a major compliance issue or that the process is completely mis-understood- user must be "pulled out" of the scenario and remediation training provided.

Some areas only have Red/Green consequences and some may have multiple red, yellow, or green replies, but we find when we use this, most folks design with more focus on the rules of engagement.

A bit "branching scenario lite", but I find that returning to the basics usually keeps things managable as the complexity of the tools or scenario itself can get some folks lost.