Female Great Tit killed by a cat

Afternoon all,

I really need some advise, there was a nesting pair of Great Tits in my mums new bird box, she was so excited.  The female was killed by next doors cat, so I said to mum to clear out the box in case another pair wanted to use it, she opened the box and there was a nest inside with 6 eggs, she threw them away and chucked the beautifully made nest. 
The male Great Tit is in the tree, constantly chirping, could he have hatched and raised the eggs alone?  Should I have told mum to leave the nest alone?  
I’m racked with guilt now and feel so sad. 
Please let me know if I did or didn’t do the right thing, I’d like to know either way.

Thank you.