Taking likes and dislikes out of the equation about each player (though I do like Scal more), our simple objective need is at the 4/5 spot. Right now, Scal's our 4th big. If TA stayed and Daniels came on, Allen would at best be our 4th 2/3 with Walker and Giddens available to play the 2/3 and House available at the 2.
Simply put, TA's (limited) role is very replaceable. Right now, Scal's isn't.