Really, Marcus Claudius Marcellus has made so much for a victory above Hannibal. His death was tragically and at the same time nonsensicall. He has got in an ambush together with the not numerous group during reconnaissance of place and has been killed. Why such talented commander has shown similar unconcern? Especially the enemy was about and Marcellus should know about it. (He specially tried to set up camp as closer as possible to camp Hannibal to limit forage the enemy.)
Probably, unconcern has appeared together with confidence of his forces. Marcellus was confident the chosen strategy and the future victory. Yes, it is possible his death put off the end of war, but I think, that not much more. There would be no victory at Zama in 202BC; there would be other victory in 203 or 204. The death of Marcellus has put off a victory no more than for 1-2 years. It is difficult to answer such questions unambiguously.
All right, this my opinion only.