"If all the Muslims left Islam today, it would not decrease Allah in anyway, shape, or form."

I partially disagree with this statement. Just like any denomination, if everyone in the religion leaves, the religion ceases to exist. People need the religion and the religion needs people.
If everyone left the religion and Allah wished for the religion to continue, a new prophet would be required to re-start everything and re-issue the religion, but then this religion, by definition, would not be the same as the aforementioned and would require a new description.

However, your original statement is founded upon an absolution which will never take place anyway. Feel free to advise how a religion will proliferate and sustain itself without people.