At the moment I feel as though all are needed. Kostka and Fraser are career AHLers so its tough to say what will happen with them. The rest are still in a tryout phase for the most part.
This could easily change by the deadline depending on where the Leafs sit in the standings.
If/when Rielly makes the team I feel like he will be Liles' replacement.
I like Kostka as a person and he hasn't been playing bad by any stretch of the imagination but I'm just not sure if he fits long term. I'm leaning towards "he doesn't".
Looking at it from another perspective, to me Phaneuf, Gardiner and Rielly are the only true keys going forward. Franson might be included if he plays consistently.