Are the restored frequencies above 16Khz even audible?

Yes. Humans hear frequencies between 20Hz to 20Khz. Low quality audio hardware, like smartphones, can easily play these frequencies.
Unfortunately, audition does degrades with age and with exposure to loud sounds. For example, the famous ultrasound "Mosquitone" (17.8kHz) is clearly audible to younger people, but notoriously difficult to hear for adults.
However, even if not directly heard, high-frequency content is crucial for the transient response and "spatial feel" of audio, which impacts how you perceive quality even if you don't consciously hear a sine wave at that pitch.