What if you see Necrolyte with Scepter, Hex, etc. Almost half your hp and he ulti, what happens?

What do you expect this to be? Do you expect a fixed situation whereby you can predict what will happen next? If that's the case then quit playing computer games, pre-program your mouse/keyboard clicks and sit down there watching while enjoying coffee. Please, if you don't understand how real time strategy game works, read up in google Don't tell me your item build for a particular hero is always fixed instead of looking at what the opponent's heroes are, etc. Does that mean every time you're using Treant Protector you'll buy refresher orb when your opponent has BKB?