Quoted from Whysnow:

lol. Gary Stern ran a business. He definitely did not save anything.
Roger Sharpe > sure that guy saved pinball. Gary Stern knew how to do 1 thing and that thing was/is the business of making pinball. Pinball machines were still on route and in bars and even in homes during those dark years. Stern make some sub par games, learned how to cut costs during that time, and cheapened the entire product.
It is not like others had exited the industry because it was not profitable. It merely was not as profitable as other areas where they could leverage the same manufacturing expertise.

ANY company that came along and decided it was a market space they wanted to be in. You can easily predict the alternate history... A previous company could have started back up. Multiple new companies could have started. The reality we now see would likely not be much different in number of players if Stern had closed shop.
Do you really think JJP and spooky only entered the market because Stern was still around? They entered the market despite Stern being the big player with a history of how they act.
I gotta say, it really is not that big of a void to fill... From 2000 to 2010 they made ~30 different titles. How many of those are currently considered good? 3 maybe 4 if you are a stern lover.
LOTR, TSPP, Spidey, Tron
All the rest is largely junk titles that nobody really seeks out or rates highly now. Stern during the dark years is not very good...