I died once, from not keeping an eye on my poison resistance enough and not backing off to let it cool down the last 20 seconds. Ended up in a silly situation and hit by 2 blob's poison with my health potion on cooldown and food low. I knew I was a dead man so I ran a bit towards where I knew I'd be coming back from the portal.

I wouldn't say you cheesed it, doesn't seem like you were doing something that made the fight not really a fight. You were trying to do the fight, were learning it and just made mistakes. I bet next time you'll do it far better.

I'm not quite sure what you mean about the fairness thing. I don't think the bosses despawning is a great idea. I don't think it changed the fairness of what you did in the slightest. Your clear of the boss took a few deaths, you paid the skill and time price for those mistakes.