ATIS, the largest groups of pilots who left Monarch and are still flying with a contract saying they can return can probably be split mostly into four groups, only one of which I would have thought may have any interest at all in returning, and that is unlikely:
BA FOs - whe the vast majority of mostly younger guys who were FOs at Monarch went, I would have thought they are unlikely to return as they mostly have time on their side and can see the BA career potential.
EK FOs - mostly ex-ZB captains, now EK A380 FOs who have taken a total lifestyle change, unless they are disliking this, I would have thought bearing in mind their significant A380 bond, unlikely to return to ZB.
Easy A320 DECs - where the vast majority of departing non retiring captains went. They are current and with no bond and thus mobile but I would have thought unlikely to return unless they really don't like the Easy way.
China, Far East, Air Tanker, EK, EY etc. DECs - now debatably the group with the most experience and still flying or current on 320s or closely related aircraft and have no bonds. This is probably the most mobile group who is most likely to return but why would they?