If there is a God then promises would logically be forever.
If God is an invention, then he/she/whatever would not keep a promise. Because if the God of invention is just a figment of our collective imagination then the God they invented is like us and he/she/whatever can’t figure out from day to day what to think...
You say, If there is a God then promises would logically be forever.
Not necessarily. If He puts contingencies on it, then that has to be considered. Read my article again.