Keep Trouba. Trade Buff and Endstrom for Krug.
As respectfully as I can, you're not considering no movement clauses (NMC) or Boston's needs at all.
Buff has one for this year and next that is a full NMC. After next year it becomes a modified NMC with a defined set of teams he can be traded to.
Enstrom has a full NMC for the duration (one year remaining) of his contract. Additionally he's coming off arguably the worst year of his career (largely attributable to his family situation) so why would Boston want him at all? Krug is what, eight years younger and played better this year.
It's fun to play with hypothetical trades but they need to be realistic to some extent.
Buff probably doesn't fit their timeline or cap situation.
Enstrom is not a replacement for Krug even if he has a fabulous bounce back year, he's only on contract for a year.
Trouba may or may not want to stay in Winnipeg at all. Everyone here on this board (I'm sure there's an exception) and Jets management all want Trouba to sign an extension and play the next 7-10 years in Winnipeg. That's nice but the decision maker in the equation is Trouba.
Chevy might have the opportunity to still deal from a position of strength this summer as regards Trouba. A team that wants him that is a satisfactory market to Trouba offers up a set of assets we need/want. Trouba's value is high and he is signed for the next season plus has two years of RFA left. If I'm a team that wants Trouba I talk to him/his agent and find out if he likes where my team is at geographically and in terms of success. If he says yes, I'm moving assets for him. But that value declines with each year Trouba is in Winnipeg because of the uncertainty of retention and a loss in "cheaper" RFA years over time. Maybe we just keep Trouba for three years as a rental. I'm not sure it's the best asset use pattern available but maybe it's better than we can otherwise do.