Might still be a bit early for this. But this would certainly be a good problem to have. Monahan as an experienced guy can probably keep his level better, so if Fantilli is playing well on the first line, I'd keep him there when Monahan comes.Question now becomes when Monahan comes back do we put him with Johnson. If Chinakhov was healthy we could actually have another legitimate threat as a 2nd scoring line
My eye test still makes me think Monahan > Fantilli for the first line, but I think it would be important for Fantilli to get some continued success, so I'd make that tradeoff and try Monahan on the second unless Fantilli's play (/scoring) drops off.