Depends on the collision and the speed. And to a lesser degree the makeup of Mars’ external layers. If it’s a glancing blow – indirect – then Titan would bounce off and go into some oddball orbit of its own, if it survived. Depending on titan’s speed, Mars’ orbit might be changed – how how much would depend on the angle and the speed of Titan’s arrival. A direct hit is more problematic – it would depend a lot on the speed, as I said, but also the hardness of the crust of both orbiting bodies. The softer of the two bodies would suffer the most, but without facts, it’s hard to know. Summary: It depends. More facts = better guesses.