How much maintenance does the catch require?
Not that much tbh - I've got into the habit of cleaning (with an oily toothbrush) and spraying/greasing annually.
Is this amount of maintenance required by other car manufacturers?
Who knows? Possibly, though I suspect the potential issues are too variable to document here.
Is there a warning light that lets you know bonnet not should properly?
Is there a safety back up feature?
Nope (though not sure what this would actually be).
Is there well displayed/well communicated information to 156 drivers that the bonnet should be dropped from a height specifically?
2nd hand buyers won't know off the mark unless they are handed something in the documentation pack (and read it) or the vendor verbally passes the info on (and I've never known either happen).
All cars were subject to recall but it's the regular maintenance, checking and dropping that is key. Some people seem to have suggested that Alfa have been in touch - though that sounds like a small minority. Either way, it's too late for you and, here you are, which is where I found out about it before it could happen to me.
As you say, it is shocking. I do sympathise and I'm glad you and yours were not injured. Is the car a write off? Was the roof knackered?
If you read through this thread and others you'll see its a well worn topic. My guess is that unless you can absolutely prove that the accident wasn't down to your not closing the bonnet properly then you have no case in law (though I'm no expert).
Regardless of what car you're driving, after closing the bonnet, however you do it, you should check that it is firmly locked. Even after dropping it, I always check.