Oh gosh no!  You can't second guess!   I think we all do no matter what path we took. I believe it's a normal part of healing.  

Even for me who was at complete peace with letting Comet go because she was dying, found myself questioning my decision a few weeks later.  Thank goodness the ER vet's words still ring in my head.  "you are doing the right thing, she is dying and doing anything more isn't good for her." 

I think because we just miss them so much, we start blaming ourselves in a weird way.  

zeuspod wrote: To this day we wonder if we had not chosen to proceed with the TPLO surgery whether the illness would have stayed dormant for awhile.  And, when it did show up whether it wouldn't have gone gang-busters if his immune system wasn't weakened and maybe we could have treated it…. 

I totally understand how you feel!  I had one throw a clot after an ACL surgery too.  She died when they went to get her to go home. I had her leash in hand ready to leave.  And she died.  So, you can imagine how petrified I was to have, not one but two ACL's TPLO surgeries on Comet!  Even my vet wouldn't do the surgery because of my previous dog dying in his care.  He recommended a specialist come in!  And he knew I wouldn't leave Comet overnight.  If they are going to die after the surgery, I better be there!  So, he let me take her home about 4 hours after surgery.  But one thing I learned from my mom having bone surgery, throwing clots isn't that uncommon. It's carefully monitored in human bone surgery.  Unfortunately, we've even seen it here with amputations. I'm well aware of it now.  So, I don't look back with as much blame on myself.  It just can happen.

Back to Spencer's moms question...if you feel inclined - here is a 24 minute seminar by a well accomplished conventional human onc that speaks to how little we know about cancer because of it's complexity.  He talks of trials done in humans with carboplatin specifcally.  He talks about trials done with chemo without placebos in the US and then trials in other countries done with placebos.  It's enlightening or at least I found it enlightening about chemo.