They can surrender, then swap in a POW exchange.
Russians should hold out for 10 Russian fighters for each foreign NATO advisors (British, US, French, German, etc.) released.
We are talking about Ukrainians who have not surrendered, right? Why allow them to leave without taking them prisoner and then confirming that each prisoner is in fact Ukrainian (and not one wanted for war crimes)? It’s a rather odd and, as far as I am aware, unprecedented proposal.