Sounds to me like a couple of vets need their licences pulled.  :x  :x

If there is any chance at all, that the calf is alive, it needs a c-section.  If the vet won't do it, send him down the road, load up the cow, and haul her to another vet if necessary.

If the calf is so obviously dead it stinks, then it needs to come out in pieces.  It can be done, but it's a dirty job.  To leave it in there is inexcusable.  That just puts the cow at risk.

If you don't like what the vet is planning to do, and you think they are making a mistake, STOP THEM.  It's your cow, it's your money, and you don't have to accept nonsense like this.