Johansen and Panik for Martinez seems fine, if LA retains a whole lot more.
Djoos got 7 points in a 15 game stretch last year, once his leg was healthy. Martinez has six points through 16 games this year. Not a big enough difference to get seven years older or four times more expensive at #6D. Martinez used to be tough, too, but he's on pace for 50 hits if he plays 82 games this year. Djoos has 40 through 108 games. Not a huge upgrade, when some guys get 250. Yes, Martinez eats a few more minutes, but he's twelfth on a bad team in corsi, so maybe he shouldn't play so many minutes. Djoos led the Caps in corsi as a rookie. Zone starts helped, sure, but playing with Orpik arguably might not have helped much.
Martinez is a little more clutch than Djoos, so far, but he's slowing down, so who knows? Djoos has nine points in 12 games for Hershey this fall and is going to get a chance in the NHL somewhere. If it's not Washington, then the Caps should consider trading him, sure, but only for someone better.
If there isn't a trade out there for someone who is definitely better than Djoos right now, then they should keep him and wait for an injury to open up a roster spot.
You mention cap space as a motivator. I don't know if you saw the Djoos for Honka trade I just posted, but it leaves the Caps with enough cap space to ice 22 guys when Panik is healthy. Since injuries are a given in the NHL, that should be good enough? Don't panik.