If you were wondering what "better to die on one's feet than live as a slave on your knees," this is what it looks like sometimes.
You only need to go back to Aleppo in Syria, when the Russians did the same strategy and completely surrounded Aleppo. They opened a humanitarian corridor to allow both citizens and surrendering soldiers to leave. After closing the corridor they dealt with those left to fight.
That is what they are doing in Mariupol, only this time any surrendering soldier leaving will be checked for the Azov Neo-Nazi tattoos, and will be eliminated. That is why there will be no surrender. The Azov off battalion controls the city... At least for the next 24 hours.
The citizens could get out. The Azovs were not invited to leave I would guess.
Why would you surround an army and let the army leave?