It all depends on your expectations for this season.
Most posters want the habs to go for the cup right now. This year.
Trading 14 to get something because he might walk will weaken us.
A UFA to be Plekanec will not give us a player that will be more useful than him to this team.
If Bergevin does not plan to extend Plekanec and wants to go for the cup, another option would be to swap Plekanec with another UFA to be of equal value and try to sign back the said player before he becomes UFA next summer.
A Plekanec-Backes swap becomes an interesting idea, if you are ready to take the risk that Backes might leave for nothing next summer.
Fetching draft picks for a UFA to be is ok, but risking to lose a player for nothing to go for the cup right now is not a bad option IMO.
Then again, would you rather have Backes or Plekanec on that team, and do you think this year could be the year ?