Possible CSA victory on the battlefield, whilst CSA defeat everywhere else. The South probably had no one better than Davis to lead them as President. So without him the CSA could have split up under the strain of the war. If so then the various states are easily gobbled up by the Union one by one. But without Davis you want have him interfering with his generals, especially the likes of Joe Johnston, whilst supporting others like Bragg. This could be very beneficial from a military standpoint.
The loss of Lee isn't as huge as it may first appear. It means no Gettysburg for starters. The war in the east becomes a frustrating endeavour for the Union in northern Virginia, although it does depend upon who leads the Union armies in the eastern theatre. Meanwhile, out west, overall the war is still decided upon whether the CSA invades Kentucky. If it doesn't repeat its idiotic invasion of Kentucky, then the Confederacy may survive the war, otherwise the Confederacy is still doomed.
The loss of Grant, again, isn't that much of a huge loss in the long run. There are other highly competent Union officers out west more so than in the east. It is, though, quite possible that no single Union general stands out to become overall General of the Army unlike Grant. So you could have, say, Thomas or Sherman out west, doing very well thanks very much, & likewise Meade doing the same in the eastern theatre.