...me thinks an autopsy is next. Went down about a foot and a half. Let me tell you, without a chain saw, this ain't easy. Anyway, this is looking straight down. All soft bits removed from the center. Do I waste any more time and effort cutting?
Not sure if you should cut more or not, but definitely keep us updated! It looks like the middle was mushy so I hope that doesn't mean it's definitely a goner. I can only imagine how hard that must have been to cut without a chainsaw, that is a thick trunk!
I really hope it pulls through!
You may want to cut a couple more inches down to remove some of that gooey rot in the center then spray with copper fungicide and let the rest of the gooey part dry up. It looks like you may have a chance, but have to get the growth resuming quickly seeing as summer is half over. Good luck, hope it recovers for you!
PS-Maybe a 5 gallon bucket over top of the trunk would help avoid more moisture when it rains.