Leaking?
I would think you would want to fix the loose keel, as the screws which hold it in place (or are supposed to) make holes in the canvas, which are potential leaks. If the troublesome spot is at the bow or stern it should be a relatively easy matter to work some bedding compound or other goo under the keel and fasten it back onto the stem where it belongs, probably using new or renewed screw holes. If the loose area is amidships you might be able to do the same, but screwing through ribs from the inside into the keel. I would make sure there is plenty of bedding compound in the holes and under screw heads. The real question may be why this has happened - rot in keel or stems so fasteners let go? Undoubtedly you will find out at re-canvasing time.
Don in Vermont