Yes the team needs a CB. I guess people already forgot how until last season the team rode the wave of uncertainty and poor planning into defensive problems and panic purchases.
Team only has 2 reliable CBs, only one of which (Pique) is a long term player. Mascherano is already 31 years old and the planning for his eventual replacement needs to start in earnest.
Aside from the 2 first team players, yes they have depth, but it's suspect at best. Mathieu is solid on his best days, really shaky on his worst. Oh, and he'll be 32 years old in a month. Bartra is young, but doesn't seem to have a future on this team. Vermaelen looks good if healthy, but seems to not be healthy all that much.
Honestly the best course of action for them is to replace two of the three bench CBs for one young and good CB to rotate with the starting pair. Keep the other of the three as the 4th depth CB.
My vote is for selling Bartra and Vermaelen, sorry for Verm, but his injuries just makes him too unreliable. Mathieu offers some flexibility too.
Pique, Masche, Gimenez/Laporte, Mathieu.
Edit: I'll add a caveat. If this injury to Verm is minor and he comes back and plays the rest of the season, then it might be better to sell Mathieu instead of him and have Verm as 4th depth.