I have done this with some success.
Stop giving milk replacer and give the calf jello water, a full small box of it, mixed with the electrolytes. It will give him calories and keep him hydrated. Get some SMZ tablets and dissolve 2 into the jello water. Give this to him by bottle or tube him. He'll need at least 3 pints of this several times a day. You can give him a pint here and there thruout the day if it's easier on him. Right now I'd get at least 3 pints down him immediately. He's got to restore his electrolyte imbalance and get rehydrated right away. Also, get some spectam and squirt that in his mouth or put it in the bottle of electrolyte mixture.
I normally don't withhold milk during scours, but in a case like this, I certainly do. The replacer may be irritaing his gut at this point. Wait until he has some strength back before you introduce the milk. I'd give him jello water for about 3 days.
And push the probios...I mean lots of probios!
The calf sounds to be on his last legs. Whatever you try may not make a bit of difference, but everynow and then, one like this can be saved. I've always thought that when one gets down like this, what have you got to lose. Go for it...pull out the stops. Try whatever makes sense to YOU. And remember this...not all of them will live, or were meant to live. But those that keep trying to live, I keep trying to save. I understand where you are coming from with that one.
Alice