I'd prefer to keep Graf and have him in our top nine because it's important to have players with different and useful skill sets throughout your lineup.
That's not to say he's not a good trade candidate. But I just don't understand why you think it's worth trading a player like him, who will have value and appeal around the league even after he signs his next deal, in exchange for "a placeholder defenseman."
That's just bad management of assets.
Even if you're trying to move up the timeline or whatever (which I disagree with as I see zero evidence that Grier's job is on the line), the problem is that Graf is a very useful player right now for this team, and removing him in a trade for a guy like Rielly means any gains from Rielly—which will also come with defensive issues, surely—are going to be offset to some degree by losing Graf.
And if you know you're likely to have to buy out the player in a couple years, that's even less reason to give up a useful young asset in such a trade!