For exporting WMO models to Blender you can use the script provided in our downloads section. For everything else... M2 models can be converted to common formats in different ways. With the support of animation, (if that's what you need for your necromancer) you'd need to downport M2 model from Wrath+ client to TBC format (there is a 010 editor script for it, created by Koward, as far as I remember), then you'll be able to open it with a tool called MDLvis and convert it to Warcraft III .MDX file which has a lot of plugins for all the editors.
Also pay attention to Machinima Studio. I believe it can do stuff like that pretty well. Though, it is not free to use. There is a trial extender, yeah, but we do not encourage piracy here.