Hm… seems to be a recurring topcic… Deadline for Librem5 pre-orders? 
As can be seen here (3500 phones ordered, almost $2.5 million raised) it would be rather stupid to close pre-orders any time soon. June crossed the +4% mark, and I think July and August will be the same, after they send news out that the dev boards have been shipped. It’s in the companies best interest to have as many pre-orders as possible.
I would expect that you can at least pre-order until end of September, but possibly you can even order (not pre-order) in December, as they likely will order some for stock.
Still, I’d order as soon as possible, as this helps the company the most. Also, it’s not unlikely that the price will go up, as a marketing move: “Order until Sep 30 for $599, or after that for $699”.
Long term, the price will hopefully go down, but I don’t expect that in the next 12+ months.