If you're sandboxing Google play services, you are, by definition, still installing play services. They are still running, but are sandboxed. So I don't see how you see any less battery drain.
I run MicroG instead of the proprietary Google play services, and while I do see a bit ofl an increase in battery life for light usage, for medium and heavy usage it's pretty much the same. Admittedly my battery is pretty old.