This would only be a good move for the Senators if there is a refusal from the ownership group to allow a Colin White buyout.

The Senators have lots of bad contracts. They are supposedly under a budget, They also want to add a big time forward (rumored to be Fiala) and a top 4 defenseman. If they can buyout Colin White, then the difference in salary between White's buyout and Monahan's salary is approx. 4.7 million dollars (since Monahan eats up a roster spot, which saves 750k+). With Monahan being a reclamation project that has no guarantee of succeeding as a top 6 forward, there is no way the Senators could do that.

Zaitsev for Monahan, I think they would do if there is no market for Zaitsev. Zaitsev is buyout proof due to his signing bonuses, and it would get the Senators out of the second year of his contract. The difference between the two would only be 1.5 million in real cash. At the same time, it would lower the Flames cap by 1.5 million, and get them the better player (even if the internet hates Zaitsev).

Murray for Monahan also works for Ottawa, but I don't see why Calgary would do that. Zaitsev at least makes some sense, Murray makes zero sense.