You assume to know what we cannot know and will never know for sure: That Zelensky was given an offer to flee.

We know from a leaked phone call that the US told Zelensky directly that Ukraine would never be allowed into NATO, but publically the US would always hold the door open.

It is just as easy to speculate that the US made a public offer to Zelensky to flee, but in private told him if he did the US would not protect him.