Arsenal urgently needs both of players. I think they want to recruit Wirtz. Their poor performance after Odegaard's injury caused this. They lack of quality in CAM. So, they think Wirtz is their answer to strengthen their CAM.
I don't think they lose a match without Odegaard, do they? I think the only disappointing result was against Manchester City and you could argue the red card affects them more than Odegaard's absence. Even if they do look for Odegaard's replacement, they have to adjust by preparing different tactics since injury can happen at any given time. It's not like your new player will always be fit either.