I'm not sure where he went. I've never had a random dragon attack in Falkreath (and they don't spawn anyway as I've only done MQ up to Whiterun) and don't have Dawnguard installed.

I've no idea when he stopped showing up, honestly. Maybe about 20 levels ago? I just happened to notice very time I go to Falkreath, he's no longer there. To ensure, I waited every hour for a complete day, and nothing.

Anyone else experience this and have a clue where he went?

It is possible wandering wildlife got him when you were in the area, in the worst case its also possible he just fell through the map.

These kind of things happen sometimes Im afraid.

Maybe he rejoined the Stormcloaks.

NPCs can die in Falkreath from the various animals that wander into town.