I really think they are putting a package together and Zacha will be a piece. When people in the Vancouver media even suggest Zacha as a trade target it always feels now like the management and media are bracing the fanbase.
There has been smoke around Boston and Vancouver since January and when the Bruins and Canucks both fell out of the standings, it makes sense that they put any trades on the backburner.
You're guess is as good as mine as far as what Pettersson is now worth but this management team has a track record of trading away players for pieces (Horvat, Miller for example) and then immediately shipping those pieces out for the asset they want (M.Petterssen, Hronek, etc).