Oh poor kitty. Being bitten by a poisonus snake. But what can you do after being bitten? Cats only weigh in from around 3 kilo to maybe 7 kilo. They are small enough that bites are going to be far worse than for people. At least the owners had enough thought to do what they thought was the right thing for the kitty. Could they have save it had they discovered the bite sooner? Maybe. Maybe they discovered the bite within hours. Bites like that are going to be very noticeable in matter of minutes and not days.

As for neglectful owners, some do not take very kindly to your generous offer. Some even get very hostile!! Best to call your humane society. Sometimes this is all you can do. No good deeds go unpunished