Poor little thing! I hope you can get it sorted with the pet store and it works out the best for both of you. I'm so sorry for the loss of Stig... it can be hard to bond to a new pet if you are still grieving the old one. When my pig Frenzy died last summer, within a couple of days we went out and bought another pig. My rationale was that I didn't want Linney (surviving pig) to be alone for too long, and my kids were so upset that I thought bringing home another pig would give them something to be excited about rather than simply mourning. But I really, really wasn't emotionally ready yet, and nice as our new pig Sundae was, it took me awhile to actually bond to her and feel like I loved her in the way I loved Linney and in the way I had loved Frenzy. At one point when we had to postpone introducing them to deal with a medical problem with Linney, I was about ready to take her back to the store because we were still in the 14 day return period and I felt like we got her for Linney, but Linney wasn't able to meet her, so what was the point? However, I'm very glad that I stuck in there with her, because she is a very sweet girl in her own right and I can truly say that I love her just like I love the other pigs- it just took me time to be ready to take that emotional leap again.
I guess my point is that I can understand not feeling ready and not wanting to go through it again- it is heartbreaking to have sick pets. Right after Frenzy died Linney had to have abscess surgery and I was a wreck... I really just felt that I couldn't handle having a sick pet again and I couldn't stand to lose them both in a month. I can see why you feel the way you do, but I do think that if you see this little guy through you will eventually grow to love him, once you are a little more 'ready' to bond.
((HUGS)) and hope it works out for the best for both of you!