In several of my recent games (as tanks or durable melee), I've been accused of running too early or not being in the fray when my team needs me both during large and small team fights. Usually I'd just figure that I'm an easy target to rage at by somebody who has never once played a tank themselves, but I'd figure I'd see if their a hole in my tactics just in case.
First let's look at a classic 5v5 team fight. Now from my perspective, I just initiated on the enemy, took a load of stuns and debuffs for my team, cleansed, unloaded my skill bar, and made it out with about a quarter of my HP left. Unless I'm severely wounded and out of MP I usually hang around during the fight (but not in the front until I get more of my HP back) and continue using my skills as they recharge. If a fight goes poorly I'll hang around and try to slow the enemy during our retreat, or even sacrifice myself to get others out alive; I will however bail on my teammates if they're obviously going to die and won't do anything to try and escape. Would staying around (and most likely dying in the process) be worth it? Would me being up front until the moment I die turn the fight in our favor?
Another scenario is that a DPS tries to gank an enemy and two more enemies flank us. I can use all my skills to try and damage the enemies and support my ally, but I see that it's a hopeless situation so I high-tail it out of there while the DPS stays to try and finish off an enemy. Promptly, the now-dead DPS claims that it's my fault he died and that one of us should have gotten the kill. Is it my job to go down with the ship to ensure our team gets one more kill even if we both get killed in the aftermath?