First of all, there is no way of knowing that. Second of all, the 1st round pick we are traded to supplement the team was an extremely late round picks anyways.
Not saying that Chevy should give up a 1st every year for help, but the Stastny trade made sense, and I would do that trade every day of the week. If we are in a similar position this coming TDL, and a high-end center is available would you trade another 1st for the help? Have to strongly consider it.
No, absolutely not. I asked a while back for recent examples where picking up a rental probably made a difference between winning and losing the Cup, and the only one that was mentioned was the Kings picking up Gaborik in 2013-14. And it's worth noting those Kings since then have failed to make the playoffs twice, and been blown out in the first round twice. Short term gain for long term pain?
You also have limited time to incorporate the new player into your team's system. It might work out in time, it might not. If a team has done well enough going into the playoffs that they're considered a serious contender, why risk messing that up by introducing an unknown quantity? Plus, what does it say to the guy getting pushed down? Thanks for getting us this far, but now we want you to spend more time on the bench because we just think you're not good enough? I wonder what Bryan Little is thinking this season now that he's back up to 2C? Will he play a relaxed, confident game or just be looking over his shoulder all year?
Just say no to rentals, IMO. As Mortimer said, keep building for long term success and many opportunities and one of those times you might get lucky.