He had a follow up visit to the vet today, who told me he is doing remarkably well. He wants to see him again next week and I have to carry on with the antibiotics until Thursday.
We talked again about the time limit before going in with the sows. He says that sperm dies after 3 days, so even if there was some left in the conduct, it is impossible that they could get a sow pregnant after 6 weeks. I told him about cases on this forum and he said it could only happen if the operation was badly done. I asked him to vouch for it and he told me, that in MY case, after he already made a mess of sexing mum, he wasn't going to vouch for anything! LOL
I am just glad Vashtian is healing well. He is such a good patient.