I just think it is widely optimistic to think that Pence is saving it for anything. I doubt he sees any red lines at all. To get this far with this administration you have to have rationalized and internalized a lot of shit, I don't think Pence sees the existence of an exit ramp. If Trump fires Fauci against Pence's advice, I don't think that changes anything for Pence.
That said, I am not at all convinced it is Pence that is advocating for Fauci, it could also be McConnell. McConnell is really paranoid about the idea of a Democratic sweep in November on the back of this, and firing Fauci would not help his cause.