Who else are we going to sign with 1 day of the transfer window left?
Obviously it's a disaster scenario if Chiellini has a notable injury, but it's also not workable to have a pile of starting-quality players for each position, eventually they grumble and want to play somewhere, or they stay and the performances are below par. You can't get a happy medium so have to resort to less talented players as back ups. Someone like Bruno Alves would simply be a product of the situation, the club would never be interested in him if three starters were not injured and one wanted to leave.
And no, I don't believe for a minute it would be worthwhile trying to force someone with Benatia's personality to stay, he's a hothead.