Songo'o and Dickov leave Palace
The pair had come to the end of their loan deals and boss Neil Warnock has chosen not to extend any further interest in them.
Dickov returns to Manchester City having made nine appearances for the Eagles.
Songo'o, who also made nine appearances, looked to have forced his way back into the reckoning before Christmas.
However, his start in the home win against Plymouth was his final appearance and he now goes back to Portsmouth.