An interesting problem of low fuel temp jtr, but normally the flight manual states the limiting value (from memory JP4 is most critical). If the minimum fuel temp is reached then the aircraft must descend into warmer air; crew action required.
Even more practical, with one engine inoperative I presume that the aircraft would not sustain very high altitude (low air temp) and with drift down / cruise in warmer air at lower altitude the fuel temp problem is self correcting.