It'll keep continuing until you get one FPS and no audio without paying for premium.
Clever.
Since I almost always on VPN, I sometimes go even lower, most long vids and podcasts I play through NewPipe without video at all. The only thing where 1:1 resolution match with the uploader matters for me is tutorials on software usage and coding, where I need to see interface and text clearly. 720p sits neatly between these two, but I am a man of extremes.