The magma casting time is so small it isn't that hard to dart inside and magma someone before he does a take resist back;quaff resist. So unless your target was spam quaffing resist potions to keep it up 24/7, he can be surprised ganked by a warlock. So spam quaff SA if you want to avoid voodoo. Not to mention that SA devices(staves/wands/scrolls/scripts) are far more common than RE devices.
And yes, sanc from a law NPC would have saved you. If you die to a non doll voodoo with high level sanc up, you would probably die from 1 single hit from any weapon(even ranged), that's how crappy your HP pool is.
As for the whole dramatic scenery of...
[--- ---] Pyras - Alone in Pyranthia, fighting darkness solo!!~11oneone
get some allies to help you gank a shaman.
PS: While voodoo does ensure infinite range for a gank, it doesn't ensure that your enemies can loot your corpse. So it's just a kill most of the times. Find a way back to life and get back your things.