I am so sorry you got such awful news with Zola. We have been down the same road with our Chloe this week. After 13 days of stasis she went back to the vet and he found a large lump under her right front leg. Initially he thought it was a tumour but did a biopsy and found it to be a rather severe tracking infection.
I hope you and Zola are able to enjoy many pain free days together, he is a most beautiful little bun. My thoughts are with you.