Can Emrakul's Evangel save me from "destroy all creatures"?
Unfortunately, no. If you use that ability in response to their spell, you still lose everything. Here's how it works, assuming nothing else happens:


They cast Wrath of God (or some other card that destroys all creatures). It goes on the stack.
You respond by activating Emrakul's Evangel's ability, sacrificing some number of creatures. It goes on the stack on top of the spell.
The top thing on the stack resolves. That's Emrakul's Evangel's ability, so now you get your 3/2 Eldrazi Horror tokens.
The next thing on the stack resolves. That's the Wrath of God. It destroys all creatures, including the 3/2 tokens you just created.


If you want something to protect you from that kind of situation by giving you replacement creatures, it generally needs to be a triggered ability. For example, Abzan Ascendancy gives you Spirit tokens when your nontoken creatures die.