I'd also take the trade. Since returning from yet another groin inury, Lehtonen has gone 2-5, 2.71 GAA, and .886 Sv%. The Stars have been scrambling and are looking like deadline sellers, so I don't think things are going to get that much better in Big D. That means losing Lehtonen will probably be a wash in terms of W and L categories, while at best will bring you marginally better GAA and Sv%, assuming the Stars right the ship a little. In contrast, Kessel is going to be a big help to you in G, A, PP, and SOG. I don't think you are going to win the average H2H matchup on the merits of goaltending alone, so bulking up in 4 out of 12 categories with Kessel while minorly downgrading 3 goaltending stats is a win.
1 yr league, 10 teams, H2H points: G(3), A(2), PPP(1), SHP (2), SOG (0.2), Hits (0.2), BKS (0.2), W(5), SV(0.2), GA(-1), SO(5)
Roster set daily: 10 F, 6 D, 1 Util, 2 G, 3 BE, 1 IR
Forwards: Tavares, Ovechkin, Ribeiro, Parise, Benn, E. Kane, Skinner, Brown, Backes, Steen, Tarasenko, Landeskog, O'Reilly, Saad
Defense: Letang, Phaneuf, OEL, Streit, Carlson
Goalies: Price, Rask, Kiprusoff, Emery