If this is true then they are definitely worried, because Ryanair never bothers to send out or make any memo's if they are not seriously worried. Ofcourse there might be some who want to come back, as there always are, but not the numbers that are leaving now. These memo's hardly ever contain the truth. And oh yes Ryanair is a very caring company, but not for things like their pilot workforce or other employees.
So all and all it is a good sign if you ask me. Interesting times ahead for the Ryanair pilots.