Just like many other players, Benzem chose money and he joined Arabian teams when left he is getting old to earn more money there.
I think Benzema made a wise move and Real Madrid should now hire an alternative player for this position. Mbappe is the first priority and I guess Mbappe can fill Benzema's position at Real Madrid perfectly.
If Mbappe's transfer to Real Madrid takes place, a football player who will play successfully for many years as Real Madrid Benzema will be brought to the team. I believe Mbappe will outperform Benzema. What he's done for PSG is obvious and he's a perfect player statistically.