What exactly is the difference between followers and hirelings or henchmen?
I know that you automatically attract followers after a certain level and acquiring a domain. Hirelings can be acquired at any level as long as you pay, correct?
Also, is there anyway to get new followers should your perish?
I'm not an Autarch, but this is how I interpret the rules/play them in my own games
Hireling is the uppermost category under which the other two categories fall. You have to seek them out, convince them to work for you, and pay them wages. They will do only the job you hired them for, no more no less, and they'll never follow you into a dungeon. In the case of mercenaries, you've hired them to fight for you, but they're not interested in the extra level of danger that dungeons represent. If you fight predominantly outdoors, mercenaries and henchmen will seem very similar.
Followers are a special kind of Hireling. They seek you out, so you don't need to find them or convince them to work for you. Some classes also don't have to pay their wages, but most do. Other than that they function exactly like hirelings, specifically mercenary hirelings.
Henchmen are personally loyal to you not only because of your charisma, but because of your promise to include them as stakeholders in your adventuring company (the fractional share of loot). It's this opportunity to profit off of lucky endeavors that gets them to follow you into dungeons. They're pretty much up for whatever as long as it isn't obviously dangerous/exploitative and as long as they keep getting their share of the loot (plus a monthly wage).
Jard has aptly summarized this.
I'll add that Henchmen can, later in the game, serve usefully as vassals.
Thanks, guys. I appreciate the clarification.