That crack can definitely be fixed, but it all depends on if it's worth the effort to you.
I have made bows of osage with some serious cracks and a good way to fix it would be to grind down the limbs much thinner and then laminate another layer of wood over the newly reduced limbs. You could use a layer of mulberry, hickory or even bamboo for the new belly. Since you planned on a possible sinew job, you then round the edges and have the sinew over lap the sides, thus covering the glue line between laminations and the sinew overlap helps to hold on the lamination.
Another solution is to grind the limbs thicker and reverse the bow, addign a sinew back. In other words make the belly into the back and the back into the belly. Simply sinew the belly as you would the back, and presto, problem solved. All Asian horn bows have the handle riser glued to the back of the bow rather than the belly. Once the sinew cover it the whole thing holds together incredibly well, provided you did a good job sinewing.
All this dramatically increases the work time, but you could still end up with a very viable weapon. It all depends on what you want.
If you are want a really easy way to laminate slats of bow wood, in a Primitive way, then use the asian horn bow method of cord wrapping and hide glue. They have a special wooden lever that a 1/4 inch rope is wrapped around the pieces to be joined. Usually one wrap per 1/2 inch of bow length is used from one end to the other. The lever wraps the rope so tight that it actaully cuts into softer woods and deforms them if you are not careful. It is much better than C-clamps. After it is wrapped simply heat up the parts slowly with steam from a tea pot and watch the glue joint. When the glue joint exudes the excess glue and the glue line is thin enough remove from heat and let it dry for a couple of days.
Here is a you tube vidio of the lamination and rope clamp method used on a korean bow...
http://www.youtube.com/watch?v=E3cjk3-AHcI&feature=relatedand...
http://www.youtube.com/watch?v=93EoM77bCVc&feature=relatedIt takes a while to get to the part about cord wrapping the laminates together but the whole video is really interesting. It might prime some new ideas in you and expand your bow making skills.