Tools You Need

Cascview Heroes of the Storm 3DSmax 2014+ (Student license works perfectly fine) M3 Import Script

Model Extraction

After installing all the required tools above, we can finally begin. Firstly, open up your Cascview and click "Open Storage"

Navigate your way to your Heroes of the Storm folder (Program Files/Heroes of the Storm/ in my case) and it should begin loading your client's files. Afterwards, your Cascview will look like this:

Next, we will find a model we want to extract. For now, we're going to extract Arthas. Navigate to his .m3 by following: mods -> heroes.stormmod -> base.stormassets -> Assets -> Units -> Heroes -> Storm_Hero_Arthas_Base.m3 Right click the .m3 file and press "Extract ..." and you will be met with this screen

Extract to your desired location and fire up 3DSMax.

Importing M3

After Max launches, click the little "hammer"(Utilities) icon to the right and click MAXScript and then "Run Script". Assuming you already extracted the M3 Import script to your 3DSMax folder, you should see something like this:

Open the script and head down to your Utilities drop-down menu and click M3 Import. The script should load and a bunch of check boxes should be filled. UNCHECK SC2 Art tools, Volume Targets and Hit Tests (these are nulls and never useful). Hit "Select File..." and locate your Arthas.m3. After your options are checked and you open your Arthas.m3, click Import. 3DSMax will either have a seizure or load up like nothing. Just be patient either way. Once it's done you should see your Arthas model in all his A-pose glory.

Exporting

Now that he's properly imported, it's time to export him to .fbx or .obj or whatever you need. For now, we'll keep it .fbx. Click the 3DS icon and click Export. Save the file as type .fbx and click "Save". Export options shouldn't be too much of a big issue as I've had no problems with default settings. Hit Ok and ignore any warnings dealing with Targets or Particles. Congratulations! You ported your first Heroes of the Storm model.