I think we need Evans even if Stones stays.
If we keep Stones (which I'm not convinced we will) I'm actually not arsed about a defender. Browning and Galloway are decent back ups, and if one of them has to step in then they have to take their chance.
I'm struggling with your thinking here chaps. Galloway and Browning would surely benefit from being out on loan: making 40 starts in the Championship has got to be better for their development than sitting on our bench every week, getting ten minutes every fifth or sixth game. To facilitate this, we need to bring in a 3rd CB. If the 3rd CB is going to be useful, and is intended to play semi-regulalrly, he needs to be better than Jonny Evans. Equally, if the 3rd CB is NOT intended to play much at all, then why the fudge would you spend £8m on him?
Evans on loan as 3rd CB I would be ok with ( presuming Stones stays). Evans as a starter? No thank you. Evans as a permanent transfer? No thank you.
But would you stifle the development of Galloway and / or Browning by asking them to be the 3rd CB in the squad, on the basis that you want Jags to make 40 starts because he's still tip-top?
Obviously there's no sense in spending £8m on a no-mark like Evans to sit on the bench as 3rd CB - you'd effectively be paying out a wedge to buy the flexibility needed to loan out one of the youngsters.
So you could take the likes of Evans in on loan - at least you wouldn't be buying him - and loan out Galloway (for argument's sake) for as long as it takes for him to be ready to come in and take over from Jags, or you can buy/loan in someone young and upcoming (but older and more experienced that Stones) who will genuinely compete for a starting spot fairly quickly.
In my humble opinion, if we are considering paying anything like an £8m fee for a CB it shouldn't be for someone who ISN'T going to push, and eventually take over, from Jags. Otherwise we will have to pay out AGAIN in a couple of years to replace Jags (unless we get lucky with Galloway or Browning). We just don't have the money to spend £8m on someone markedly below the standard of Jags and Stones AND still bolster other areas of need.