I believe there are a few human enemies that respawn infinitely, yes. The forts in Marston Avenue and Stokke Hills should be reoccupied by a fresh group of bandits on a regular if somewhat random basis, the lone freebooter in northwest Watery Eyes is stated to respawn roughly every 72 hours, and there are probably others. As for missions, City Hall probably never runs out of bounties for you to hunt.
There's a wiki at mastersofraana.com that you may find helpful, if you're not already using it.