Garrison

then it turns into a dead end.
Let's say you bought the Tome of Darkness. With such a poor starting point for the hero, it's unlikely you'll be able to defeat the Barbarian, even if you spend months collecting artifacts and squires.

But let's say you did defeat him, and there's a dead end – behind him is another garrison, just like the Barbarian's army. Let's say you defeat him too, but there's no way out?
You'll have to replay (or place a portal to exit behind the garrison to leave), or can you choose any garrison?