Austin Powers was a box office failure, but found its audience in the DVD market and got several sequels. Sony was also very, very smart with merchandising. They leveraged the renewed interest in the franchise to also sell classic Ghostbusters merch, and the tie ins and the Ecto coolers and the slime Twinkies are flying off the shelves. I wouldn't count on the box office being the only factor in how Sony moves forward.
The building of the Ghost Corps production company was built into the budget for the film, and was seen by the studio as an investment in future productions. There are factors that are almost anomalies in the industry which will certainly complicate the decision making process for the studio.