I won't be seeing Tali's face in my Femshep's story. I have NO IDEA what I did wrong on the suicide mission, but SOMEONE just kept dying. I picked the right people, my team was at maximum strength, we had the weapons, etc.
But as soon as I killed the human Reaper and GTFO, there was always someone dead. First it was Mordin, so I restarted, then it was Tali, then I did it again, and it was Tali...again.
So I just said "**** THIS" and let it be.
There must be some sort of X Factor I missed.
You're talking about the "Hold the Line" segment, I'm betting.
The X-Factor there is survivability/squishiness/splatability. If you leave squishies at the hold the line segment without sufficient defensive-oriented characters, some of the squishies will die. Reasoning: they don't have the know-how to handle a siege-like situation, nor the training, nor the armor/body to take more than a few hits.
Mordin, Tali, and Legion are the main squishies, I think in that order in the ME2 algorithms. After them, I know Jack and Thane are considered squishies, but I don't remember their order. That's mostly moot, though, since usually it's just Mordin who dies.
Easiest way to prevent this from happening is sending Mordin back with the crew, and leaving Grunt, Garrus, and Zaeed at the line. Loyalty obviously matters, as it does with just about everything in the suicide mission.
You don't have to do that exactly, but it's the way to play it safe. I'll note that in my first playthrough, not knowing what mattered and what didn't, I actually send Jacob back with the crew. I left Mordin and Tali at the line along with an unloyal Legion, and took Jack and Thane with me to the final boss, I believe. Everyone survived.
In subsequent playthroughs I usually send Mordin back with the crew and take Miranda and Thane with me to the final boss. As long as you leave Grunt and Garrus and both are loyal, I think it pretty much doesn't matter.
On the other hand, if what you're talking about is your taking them with you to the final boss (that is, Mordin or Tali) and they're dying after the long fall where Shepard hoists the beams off his squadmates, then that means they're unloyal. All unloyal party members die if brought to the final boss, no ifs, ands, or buts.
Hope that helps. If you have any questions, just ask.
