Janmark will cost almost nothing against the cap by the time they would need to make a move. Some team will want him for added depth.
I think Smith is probably the other to go because he's a UFA and would get more interest and doesn't have any trade protection.
But Dadonov has looked good in most games this season and is scoring again. And has only gotten to play with Stone and Stephenson one game so far, the rest being stuck mostly with Stephenson and a fourth liner like Kolesar or Carrier on the other wing. One down year on a bad Senators team won't tank his value that much.
Agreed that Smith should probably have his bags packed (if he's not gone by the deadline, then he's certainly not being brought back in the off-season), but there aren't all that many teams that can take on his cap hit outright-- things can change, but most of the teams with cap space aren't expected to be buyers at the deadline, certainly not for rentals. I also wouldn't ignore the possible fallout that could come with jettisoning one of the members of the misfit core by the deadline, especially if the team doesn't manage to make a deep-run in the playoffs.
Janmark isn't doing too hot. Yeah his cap hit isn't all that prohibitive, but so far he hasn't even been able to play up to even that.
Dadonov likewise is playing well below the value of his contract, and there's still another year left with $6.5Mil in salary owed. The last few games he has been at or near the top in ice time, so they're clearly trying to help boost his production, but I don't think the showcasing is going to distract any GMs from how he's been a passenger for the duration of his contract and, again, not many teams can fit him in outright, and those teams are the ones Dadonov can put on his no-trade list if he decides he prefers to stay in Vegas.