Bieksa waived his previous NTC when he accepted the trade here, meaning that the NTC of his "old" contract doesn't exist anymore, see the Visnovsky trade for reference. The only way Bieksa would have a NTC right now is if the NMC of his "new" contract was extended to cover this season as well. I'm not a CBA expert, but I'm pretty sure that it's not possible to use a new contract to give an older contract NTC. Feel free to correct me, if I'm wrong here.
IMO defense and physicality is what we're going to get from Lindholm, Despres and Manson, even Fowler to a degree. Vatanen has been an offensive catalyst, especially on the powerplay, which is something neither Stoner nor Bieksa will bring. The point is, Bieksa and Stoner won't bring anything special on the table, thus making the both of them completely replaceable. Manson will replace one of them, and we can get a veteran guy from the market to replace the other. At this point in their careers, Barret Jackman and Kevin Bieksa are essentially the same player, and Jackman is paid half as much.
Montour or Theo could step up and give that offensive boost, but I'd rather not rush either one of them just because it'd be convenient for us. These are just my opinions though.