I think you're assuming that all the injuries that happened somehow don't if they didn't sell at the deadline. It wasn't as if it were a firesale. Everyone but Filppula was becoming an UFA at year's end.
I don't buy that Filppula, Bishop, Nesterov, and Boyle were the missing pieces for the Lightning in a cup run last season for a second. They weren't for their respective new teams.
Now, using the cap space not bringing back all these UFAs to in part sign Girardi at $3M? Yeah, strange.
But the way the universe works, he'll thrive as a 6th dman who can play more minutes if necessary. He'll help their PK become even better, and he's a good lockerroom guy that they don't seem to have too many of on the roster.
Worst case, he's a familiar friend for Cally to hang with in the trainer's room :x