This on heroes with lots of AOE / insane damage like torturer might be completely OP, would have to see it in action to see the final result... I was just thinking of the possible synergy between this and the current Sac Stone on someone like torturer... Anyway, I think spell life leach is an interesting concept to bring back some int carries.
Also, 25% might be way over the top and 10% be more appropriate, it's hard to estimate as long as we do not see this in action...