They have a good experienced guard in Dennis, and he should be used and play more time.
No question about his capability, he really is a good guard, his team won the FIBA world cup, right? However, even if Dennis is good, he can also be a liability if their opponnents will design a play to attack him since he is a small point guard, so Raptors also need to look at that, I see Dennis as Trae young who is a liability in the defensive end.
Raptors now ranked number 12, so I think every game is important for them to at least qualify for the play-in tournament. However, missing Siakam might be a big problem for them and it started to show their real capability as a team.
I haven't seen Dennis though being attack by the Knicks in that game, maybe I might have missed it. But he has the experienced already, playing with the Lakers and now with the Raptors, so I don't think he will be a liability, if yes, then he can offset it with his offense as he is known to be a streak shooter, specially in three.
I think they know it already, and they have made the move to let go of their number 1 offensive weapon in Siakal. So moving forward, they will have to deal with it. And others pointed out, Barnes is now their main offensive weapon. But still though, it's better if they will have a complete team just like when they won the NBA as everyone is really a perfect fit to their rotation and system.