In the event that Grease was a flop (Butterflying Grease 2 in the process) it would likely not make any changes at all on the decline of Drive-in Theaters and Bowling (Both Osakadave and Emperor Norton I might agree on the Bowing issue). The primary reasons for so many Drive-in Theaters closing was Competition from Home Entertainment (Color TV's, VCR's Video Rentals) and Real estate interest rate hikes with People easily figuring that the properties can be better suited with Retail stores (I know of 2 former Drive-in theaters that have Wal-Mart Supercenters along with other retail stores currently occupying their sites), Car Dealerships, Industrial Parks, Sports Venues (It happened to a former Drive-in theater site in Philadelphia), Office Buildings for example. But don't expect Drive-in Theaters to completely die out faster (Unless American Graffiti and Happy Days were butterflied away which I think is completely full blown ASB).
In regards to what Emperor Norton I said about Bowling never catching on after Grease 2 is true as it and this is according to Wikipedia only grossed $15,200,000 ($38,204,000 in 2017 dollars) in the box office against a budget of $11,200,000 ($28,150,000 in 2017 dollars) or $13,200,000 ($33,177,000 in 2017 dollars) if you pay attention to what the IMDB posts. I do think that Grease 2 would have likely needed to gross at least $50,000,000 ($125,671,000 in 2017 dollars) or maybe more (It also didn't help at all that E.T.: The Extra Terrestrial, Star Trek II: The Wrath of Kahn, Rocky III and Poltergeist were playing in the theaters at the same time that Grease 2 was released) before it could have made any difference at all in regards to Bowling. Interestingly E.T.: The Extra Terrestrial was released on the same day as Grease 2 (It officially premiered the day before in Los Angeles).
Note - The adjustments for inflation are for March 2017 dollars.