Jonnie why give in on the hobby you so obviously loved buy one or two good koi books educate yourself some more on koi keeping and start again safe in the knowledge your up to speed on any eventuallity .
I was once the death of goldfish until my partner Val bough me my first ever book on fish health problems.
Now 27 years later though I'm still learning (you acctually never stop learning in this hobby)we have a nice pond with healthy koi in.
There has to be some little mistake you've made that can be quite symply rectified.
You kept your koi in good health what did you do that changed things look and you'll find your answer.
There are times when with knowledge arent as dark as you think.
Did you ever consider joining a koi club, you said your pond pump failed whilst you where away , they wold have people look after your pond besides its not your fault the pump failed.
The koi I see lying on the grass where in very good condition and in rude health i;e imaculate condition believe me I know a good koi keeper when I see one and that is from a person 27 years as a koi keeper please dont go knocking yourself about it.
Accidents happen , its probably a knock on effect of your pump failing that claimed them not you .
Please reconsider go though everything with a fine tooth comb and start again
rgrds
Dsve
