Shatty should still be able to provide a good return but I expect Army to sell low like he did with Perron, Stewart and Oshie.
That said, I'm more than fine with Shatty leaving. We won't be able to afford him and he's simply a liability defensively. We may need to add a PP specialist to maintain a good PP (although Petro is decent and Parayko's PP ability is progressing) but Shatty is not worth the money he will command to only be useful on the PP. 5 on 5, he's a liability.
Did we really sell low on Perron or Stewart?
Perron has been traded twice since we got an early 2nd and PRV for him. The first time was for Klinkhammer and a 1st. At the time of the trade that 1st looked like it would be very late, but the Pens hit a tailspin and made it a mid-1st round pick. The next trade was to the Ducks for Hagelin. Hagelin has been great with the Pens, but was brutal this year with the Ducks and had extremely low value at the time. I certainly wouldn't trade more than an early 2nd and a prospect for Hagelin.
Stewart was part of the Miller deal, and it is tough to gauge exactly what value we got for him specifically since there were many parts to that trade. With that said, the Sabres got a 2nd round pick for him last year at the deadline. It's worth noting that the pick is for 2017 on a trade that occurred in 2015, which is quite a bit different than getting an immediate pick. Buffalo won't get an asset from that trade for another year and likely won't see the effect on their roster until 5+ years after the trade. He signed a cheap 1 year contract with Anaheim this year, had a miserable season, and may very well be done in the NHL.
I didn't really like the return for either of those players, but the last few years have shown that we probably got fair value. Neither player has been all that good since leaving the Blues and each has been traded for low value that's relatively similar to what we got. Edmonton got slightly better value for Perron than we did after he had a career year on their team. Had the Pens not gone into free fall after making that trade, the value would have been near identical to what we got for Perron. I think the Pens got less value for him than we did considering Hagelin's contract. I tend to think Kessel is by far the driving force of that line and that Hagelin won't be more than a 2nd/3rd line guy for the next 3 years. I don't think Buffalo got better value than us, even though the Miller trade didn't work out.