I did wonder, Chris. I am sorry too that it ended like that. I know exactly how your Mum's feeling. It's just how it went with the stray that we tried to help too.Final update. We were able to get a cage trap from the RSPCA for a week and on the last day the old lad appeared and was caught. When the RSPCA came to collect him and they lifted the towel my mum had placed over the cage, the cat threw himself every which way trying to escape. When they got him to the vet it was decided that it would not be possible to keep him in a cage long enough for the wound to be treated and heal and they put him to sleep.
My mum is still feeling like she betrayed a trusting friend and their own cat still looks for her brown tabby pal.
We know that the wound wasn't healing and life wasn't much fun for him, but still...it is sad!
It felt so unfair, but the alternative was to do nothing and watch the canker eat away at him, and knowing that all the time that he was infectious and probably passing it along to other cats too.
No more pain, it didn't get any worse, and yes, it can get very, very much worse before they finally die.