The old employee wants to go back to the original unit and call the leader. The leader is in the field and will contact you later. Is there any hope?

It's hard to say whether it's useful or not, but in your case, you should take the initiative and be positive yourself. That is to say, to be a better person.

Ask the leader what he is doing back, invite him to have a meal, drink a cup of tea and send some small gifts.

To put it simply, you can only hope that you want to go back to your original company if you have a good relationship with the leader.