With Terminator: Genisys stalling at the box office, Arnold Schwarzenegger's T-800 may not be back again.

Despite Schwarzenegger's much-heralded return to the franchise after stepping away for the poorly received Terminator Salvation back in 2009, the fifth film in this 30-year-old series has badly underperformed at the U.S. box office, grossing just $81 million since opening on July 1. It's done better overseas, with nearly $200 million in the bank, but according to The Hollywood Reporter, that doesn't make a sequel certain.

Why is that? Well, the movie cost $155 million to make and many more millions to market, which means that (because theater owners get roughly half the box office) Terminator: Genisys will have to earn probably somewhere around $400 million worldwide to break even. And while that number could be in reach, the fact that the movie is going to struggle to get there means that demand for a followup could be even weaker.

That makes Terminator: Genisys a "bubble" movie, meaning that it's not successful enough for a studio to automatically greenlight the next installment, but it's also not such a massive failure that producers have realized that enough is enough. The Reporter cites Pacific Rim (which basically owes the existence of a sequel to Chinese audiences), Godzilla and Snow White and the Huntsman as "bubble" movies that have done just well enough worldwide to get the go-ahead for a sequel, while Prometheus and the Chronicles of Narnia films have not convincingly made their case.

The producers of Terminator: Genisys very ambitiously -- and perhaps unwisely -- announced last year that they were already mapping out sequels for 2017 and 2018, along with a TV show, but it seems unlikely that those plans will stay intact if the current film does not turn itself around (a strong showing in, you guessed it, China might help).

The question is, should they stop here anyway? Terminator: Genisys got poor reviews from critics and fans alike for basically remaking the first two films while twisting the continuity to ridiculous and even incoherent extremes. James Cameron told a complete, satisfying story with The Terminator and Terminator 2: Judgment Day, and ever since then the owners of the rights have been attempting to extend that story with frankly diminishing returns (at least on film -- fans loved The Sarah Connor Chronicles on TV even though it wasn't around long).

How long before this continued cash grab simply becomes embarrassing? Should the Terminator saga end here?