As far as I know there is always supposed to be a crucifix on the altar during Mass:
From NewAdvent Catholic Encyclopedia:
The crucifix is the principal ornament of the altar. It is placed on the altar to recall to the mind of the celebrant, and the people, that the Victim offered on the altar is the same as was offered on the Cross. For this reason the crucifix must be placed on the altar as often as Mass is celebrated (Constit., Accepimus of Benedict XIV, 16 July, 1746). The rubric of the Roman Missal (xx) prescribes that it be placed at the middle of the altar between the candlesticks, and that it be large enough to be conveniently seen by both the celebrant and the people (Cong. Sac. Rit., 17 September, 1822). If for any reason this crucifix is removed, another may take its place in a lower position; but in such cases it must always be visible to all who assist at Mass (ibid.).
Noel.