This has been predictable since round one, but the answer is "not well".
Elka, always enthusiastic at the sight or hint of a tennis ball, was far more interested in the ball in my pocket than continuing to sample the Rachael Ray dog food that we got in the mail for free (it was a free sample I signed up for...it even came with a coupon for the Just 6 treats)! As a side note, the Rachael Ray food is okay, not something I'd feed as food, but is a lovely "training treat" size, so I'll see if Elka is willing to work for it on walks. She's definitely environmental on treat acceptance; she'll accept a carrot for a successful trick in the kitchen, but if I try to give her a carrot on a walk? It gets dropped on the ground and she looks at me for the real treat.
I did not check the bounciness of the Petco ball, and neither did Elka. She took it, and chewed it. I tossed it to her. She caught it and chewed it. I'd say it lasted a good five or ten minutes of hard Doberman focus. After that, though, pieces were going to start coming off. Elka appears to be very good about this sort of thing. When pieces come off of an object (an empty 12 pack box, for instance), she seems to just drop said pieces on the floor and continue work tearing the object up. But, there isn't any reason to tempt fate, so when the tennis ball is appropriately ratty and compromised, I remove it from her grasp.
She does tend to look crestfallen when a tennis ball gets taken away, in that limpid-eyed, Disney creature kind of way. I diverted her attention by putting the biscuit from the above linked Petco visit picture into an empty Pepsi box and rolling up the open end, so she had to get the box unrolled and torn apart to get the biscuit out. The biscuit had an even shorter Elka life than the tennis ball did. After that, if you can imagine such a thing, it was nap time.