I also gave them up, and regretted it as soon as I saw what it showed.
I suggest not giving them up. I somewhat want to replay that mission to see whether having both the helm and the greaves unlocks that prison - it's been bugging me.
I'm one of those people who tries to collect everything possible on the map, build up my main hero as much as possible, and then go and slaughter my enemies in a massive bloodbath (so to speak). The maps can frustrate people like me, especially in the final campaign, when the last two missions end up being timed. In the second to last mission, I missed out on a bunch of stat boosts, and I had to reload the very last mission in the final campaign repeatedly with the first week of the mission because I went the wrong way, twice, by breaking through the garrisons. That said, they're all definitely beatable, so long as you can figure out what and where the objectives are and do them. ^_^
And yes, you are supposed to take out the stack of fire dragons at the end of this map. ^_^