Few things here. First off, this trade just doesn't make sense, here are the reasons why.
1. This team will have a significant cap overage, meaning they'll have far less cap room for next year. Chara, Debrusk, McAvoy, and to a lesser extent Carlo and Donato all have bonuses in their contract that they're likely, if not sure to hit. They've got 5 million in room (in real life, not in this trade), but it's fake.
2. In this scenario, you're trading for a center, who's good, but is paid a decent amount. Arguably, the Bruins top four prospects all project as centers. Studnicka, Frederic, JFK, and Donato. Maybe Donato is a winger, but still, it doesn't make much sense to me to have 19 million or so locked up in centers when you have a whole bunch coming up.
3. This screws them up like crazy cap wise. Carlo, McAvoy, Chara, Donato all need extensions.
4. You trade Krug....and you traded his replacement also.

Honestly this list could go on for a while...it just doesn't make any sense for boston. You get two good players, but it screws up the whole team.

yeah trades like this never happen but with bostons huge amount of depth in the system right now sure why not. panarin is easily the best player in the deal and wennberg is a center which the bruins need considering the age of krejci and berg. sure they have young centers in the system but too many isn't going to hurt and wennberg is well ahead of them at tihis point and still young

With the expansion draft (likely) coming up the following season, they almost have to deal both Krejci and Backes or they will lose one of 4 of their younger talent. So, yes it would take away from the cap the following year (similar to Iginla), but I still think they would have a little wiggle room - Granted, this would likely mean not being able to resign Panarin, but for me it's more about getting a center in. I know they have some depth their with the three kids, but A) none of them clearly won the job this year, they all played well enough, but none stole it. B) You could likely deal panarin's rights and re-coup a 3rd or 4th rd pick. C) I don't think Zboril is Krug's replacement. It seems like Vaakanainen is ahead of him, but it's hard to say because has been hurt.

I Posted this the other day - Expansion draft would be 20-21. They are going to expose someone presumably very good for nothing, possibly 3 players.
1) Bergeron 2) Marchand 3) Pastrnak 4) Debrusk 5) Donato 6) Krejci 7) Backes
1) McAvoy 2) Carlo 3) Chara (if still playing), Krug or one of rookie dmen

That leaves: Frederic and/or JFK whomever makes the team this year, Heinen, Bjork, Vaakanaian and/or Zboril whomever gets games this year ( & presumably 19-20 season - 70 games played combined).

It would not surprise me if a good number of the kids see some NHL time this year: JFK, Frederic, Vaakanainen, Zboril, Cehlarik, Bjork, Senyshyn and get some extended run next season as well. Best case scenario is they trade Backes and Krejci, Chara retires and they trade, or don't resign Krug and they still expose One of the young D and and three of the young forwards.

In this trade scenario they would
1)Bergeron 2) Marchand 3) Pastrnak 4) Debrusk 5) Donato 6) Wennerberg 7) Frederic/Bjork - They expose Cehlarik/Senyshyn

***thought being with Wennberg you have can keep Frederic down all year. giving him one year of NHL experience (19-20) and thus not eligible for expansion.

They don't have to protect Backes or Krejci....so why on earth would they? Protect the kids. Protect 1. Bergeron 2. Marchand 3. Pastrnak 4. Debrusk 5. Donato/JFK/Frederic/Kuraly/whoever.

They 100% do have to protect them. They have NTC/NMC. Unless they waive to go to seattle, they would have to protect.

Same with Chara if he is on team 35+ contract.

They don't have to protect them. You only have to protect players with no movement clauses. Think about the language. no movement. Can't move them under any scenario. No trade. You can't trade them, it doesn't say anything about expansion drafts. Both Backes and Krejci lose their NMC on July 1st, 2019. So no, they do not 100% have to protect them. They 0% have to protect them.

You are correct. Makes me feel better.

I'll just nip this in the bud for you all, if you want Wennberg AND Panarin, it has to include DeBrusk or another young top 6 guy. C'mon, that's a no brainer

Heinen had more points than Debrusk last year (which was way more than Wenneberg in 3/4 seasons) . JFK is also going to be a a good NHL Player. Thought process was CBJ could then move Krug or Murray to fit whatever needs you have later in the season (pick, prospect, vet) because Jones will be back and your D gets stronger. I don't think the market for Panarin is what you think it is because he has pretty much all but said he will be a Ranger next year. No reason for the Rangers to trade for him and makes it hard for a team to give up too much future for one year - Just look at what Karlsson went for and I'd make the argument he is more valuable based on position.