It's an entirely valid question, and it's possible the Habs dodged a bullet. However, the Habs are different from most teams in being almost comically weak at C and yet being in the prime of their supposed 'Cup window.' In other words, if any team is justified in making a risky Hail Mary contractual play on a KHL centreman, it should be us.
As for the Caps, if I'm MacLellan, I really do consider trading Ovechkin, who is going on 32, is coming off a relatively unproductive season (33 goals - low by his standards) and who, for whatever reason, never seems to win anything even when he has a supporting cast that is widely viewed as excellent. He has four more years on a horrible contract for a player at that level of production. Backstrom is cheaper and showing no sign of decline. The fan base is grouchy and will probably support a bold move. This is the right time to trade Ovie.
But let's say the Habs want in. Who would we send back? Pacioretty risks being something close to a lateral move, except we're getting back a player who is three years older and vastly more expensive in the short term. (Of course, you can argue that four years of Ovie at 10 mil is better than 8 years of Patches at, say, 7 mil. I have no opinion on that). And it's not clear that Patches would even be enough, given Ovie's stature and Patches' own record of playoff futility. It's not like we have the young talent to send back the other way if the Caps want to use Ovechkin to generate the next wave; Sergachev is it. Galchenyuk will not be enough either - with whom do we package him? (I'll bet Sergachev + Galy could get 'er done. Put that in your pipe and puff). It's just hard to see how a deal can materialize that makes sense to both parties.