Under the current resolution mechanics in place, SW:Pain will kill this. The effect of the Shadow Word spells resolves once it passes the initial check of a minion's attack.

You can test this effect for yourself if you SW:Death a valid target against a Mage with a Spellbender secret up. The spell is retargeted to the 1/3 minion, which obviously would not otherwise be a vaild target for SW:D. However, it will still die.