I was at the fight. Yes it should have been stopped but there is nothing to say the clot hadn't already begun to form, may sound stupid to say but better he collapsed in the ring with immediate attention than at home with no help. And no he should not have come out for the 12th, no of us know what could have happened.
I do remember him being on sky a couple of times after his op with his trainer, saying he was helping out round the gym or something along those lines.

If the sanctioning bodies really cared about fighters and not the $£ fighters could be monitored more closely but it takes money and it could also mean cancelling fights if a fighters weight is not down safely enough AND the difference between them on fight night isn't too great, they won't do that.