MB's a bargain guy. He doesn't trade away his players he let them walk (except Patch... good trade that one!)
The most obvious is Sergachev, won't expand why.
But I think a surprising name would be
Lars Eller . Now, I don't fault MB for making that trade, a 26 pts center for 2 2nd rounders is great value! Especially considering the team had Galchenyuk and Plekanec as a duo of promising prospect and solid 2-way veteran, + Danault coming in the pipeline. But with the way it went, Galch became worst every year, Plekanec fell off a cliff, a guy like Eller would have been nice to give Kotkaniemi some time to adjust to the NHL instead of rushing him.
I would probably redo the trade even knowing the way history played out but Montreal doesn't regret 2/3 core players they traded away lately (Subban, Patch, Serg).
As a fun one Devan Dubnyk was a Hab for a very short while