He'd be fired for breaking script and would never work in the theater again yet he's happy and strutting in Times Square? And the director doesn't yell at him like he had done for every other crappy thing Manero did previously? This is the most ridiculous part of a ridiculous movie.
Half because it's so insanely ridiculous, and half because writer-director Stallone thought audiences wouldn't find it ridiculous. He actually thought people would cheer for Tony being an unprofessional asshole!
Fair enough, but realize that most of us aren't privy to the backstage goings on of a Broadway show and that wouldn't immediately stand out. Once it was pointed it out, it did indeed seem ridiculous.
I'm an engineer (retired), and the ridiculousness of the laws of physics being broken are, well, ridiculous.
I think the movie flopped because it basically sucked, not the change of script at that really, really crappy Broadway play (that would have flopped - probably closed that night). I watched the whole movie to the end, but had pretty much determined within the first 10 minutes that the Staying Alive sucked.
She also didn't seem in be in any jeopardy; she gracefully leapt/danced onto the platform.
Whether it appears to you that she was in jeopardy or not, partners in dance don't do that to each other. And the movie did suck. I'll leave it at that.