The US Military, overall, will survive. But companies would like to keep their production as long as possible. For example, the F-18 have had some Navy orders as a result of the delayed F-35 program. However, additional overseas orders will help keep the F-18 run longer once the current Navy orders are filled.
Also, while most of the F-35 will be purchased by the US military (about 2000 or so), an additional 1000 is expected to be purchased by foreign customers. This additional 1000 will help in reducing the per unit cost of the US purchase of her 2000.
Overall, foreign sales help bring down the cost of what the US military ends up paying for their hardware.
You are quite wrong actually. This article talks about 22 refurbished F-16s not F-18s. The F-16s are at the very tail end of their production life. There is very little likely hood of any future large scale purchase of brand new F-16s from overseas. And USAF isnt buying anymore F-16s. The per unit of production especially for smaller order of new generation F-16s goes up considerably higher. It costs a lot more to keep the production facilities open for only small orders from overseas. That's is why Dassault closed the production line for the Mirages even though they were commercially very successful overseas.
Beside these F-16s sold to Indonesia are refurbished F-16s from older stock. It doesn't really help in keep production facilities open.
I can understand your rancor over US supplying F-16s to Indonesia to bolster their defense against China but trust me, China does exactly the same with Pakistan.