Hi Migky,
I can understand fully your reluctance to spend money on a 'maybe' possibility.
It does seem odd that Catherine would not put her father as deceased your right.
Lots of wonderings here

Why would Leonard put Catherine as next of kin and not his father or older sister?
Do you have Catherine in 1911? I saw a 'Katry' Madden (or similar) but no Maddens with her, I don't think. (am still trying to work out searches in 1911 census).
There is a George Corry/Mary A Madden marriage in 1905 and checking 1901 there is a suitable George- the couple would be very young though.
1911 George seems to be there but not with a Mary A

Have just found a death for Mary Ann Corry 22 yrs in 1907 -Prestwich registration district so that would fit and explain things but all supposition

There are a few Mary Madden marriages too- and if Mary Duffy married again that would also be a help. However, when she married William, her previous name of Donnelly is shown on Lancashire BMD so you would imagine that if she remarried again one or other of her previous names would show on the marriage list- but maybe not

Do you know if both William and his daughter Catherine married in the same church? If they had a 'family' church then perhaps, if he died, and if that was Mary Ann's marriage to George Corry or anyone else for that matter, they would also take place in the same church.
I think you already mentioned St Patrick's Livesey Street?
Well that's my contribution to the puzzle at the moment

heywood