Silver lining

Jonathan is one of the few truly admirable people in OT history. OT history is full of villains. And even some of those on God's side have glaring character flaws. In one respect, it's tragic that he died so young. 

But suppose an alternate history played out. Had he assumed the throne, Jonathan might have been corrupted. 

Or if he was David's righthand man, would their friendship sour? Over the long-haul, would he find it grating to play second-fiddle?

And even if that didn't happen, his sons and David's sons would be rivals to the throne. One or more of his sons would probably think David was a usurper. That Saul's lineage was the rightful lineage. I can imagine one of Jonathan's sons murdering one of David's sons to snuff out the competition. Consider the strain it would put Jonathan and David's friendship.

Or what if Jonathan was still alive when the Gibeonites demanded scapegoats to even the score for Saul's effort to extirpate the Gibeonites. Jonathan would be at the top of their hit list. Since Saul was dead, Jonathan would be the next best thing.

Presumably, David would refuse to hand over his best friend. Even so, what would Jonathan's reaction be when David delivered seven of Jonathan's nephews into the hands of the Gibeonites, to play fall guys for Saul's misdeeds? Once again, imagine the strain that would place on Jonathan and David's friendship.   

Jonathan died before the friendship had a chance to fall apart.