For most bike riding I consider 200 Lumens near the minimum normally speaking but a lot is dependent on beam shape and diameter. Usually more light is needed for dirt road riding as you do not have street lights or other additional lighting supplementing your headlight.

The Maglite is far from state of the art flashlight lighting these days. The 104 Lumens rating of the 3D LED Maglite makes it about mid way between a "To be seen by" light and a "To see with" headlight. It is also very large and heavy for the light output compared to many other flashlights which makes adequately mounting it on a bike more difficult. The D cells do give a long battery life though. Strap it on the bike and give it a try as IMO it is the only way to tell if you feel something with similar Lumens output will be adequate for your use.