Will we ever have phones with screens and outer casings that are resistant to scratching/shattering?

We already have that. It's called hardened glass and good build quality. If you mean will we ever have scratch/shatter-proof screens and cases, I doubt it. Anything will break if you hit it in the right way.
 
We could now - but do you know how much a diamond screen "glass" would cost? A sheet of diamond 5" long and a mil or two thick? Do you really want your car to cost less than your phone? (There's a problem, though - scratch-proof means hard, shatter-proof means soft [or non-crystalline, which is mostly opaque]. So until Mr. Scott really invents transparent aluminum that's as hard as diamond ...)

It's a lot cheaper to replace 3 for $5 screen protectors every year. As for shatterproof, use a TPU case with a lip and exercise just a little care. (The only phone I've ever "dropped" was a Nextel i35S, and I used to throw it against the wall to demonstrate what a rugged phone should be. [The battery cover would fly off, the battery would pop out, but I must have thrown the same phone a few hundred times as hard as I could - even down to concrete - and stopped using it when Nextel stopped using iDen. Driving a tank over it might have done some damage.]) But I treat normal cellpones like rotten eggs - I don't drop them.
 
I may not be the best example, because I treat my device very carefully, but I decided to stop using a screen protector about nine months ago and there's not a flaw in the glass to be found yet.
 
I may not be the best example, because I treat my device very carefully, but I decided to stop using a screen protector about nine months ago and there's not a flaw in the glass to be found yet.

Probably goes to show how far Gorilla Glass has come. GG3 has been a significant upgrade over GG2. Makes me wonder whether we'll see a screen one day that can survive minor drops without incurring scratches. Gorilla Glass 4 if it ever arrives hopefully will bring us closer to that day.
 
It's a tricky dance, the more a screen is resistant to scratches, often that means it is going to shatter easier... The two traits are kind of at opposite ends.

That's why sapphire screens aren't all over the place...

What I'd like to see are screens that are easier, and cheaper, to replace. Make them removable... Like a recessed screen protector.