You -were- asked but ignored it.
Quote from the Ascension summary: "He told her soberly that the Migrant Fleet was dying. Although the quarians had maintained zero population growth aboard the Flotilla quite successfully in the three centuries since their exile, their problem was the lack of spaceworthy vessels. They were unable to replace old ships as fast as they were losing them, and within ninety years, their population would be unsustainable."
That is very different from going extinct, which is what you said would happen. They'd lose ships, their population would not fit into the remaining space and then there would be trouble... but at no point would they die out. He was talking about the fleet (the ships themselves) dying, because they are too old.
No mention of epidemics either.
What do you think "our population would be unsustainable" means? Do I need to google you the definition of that now, too? Their population. Would. Be. Unsustainable. It cannot be maintained at the current level. Therefore, it would decline, ultimately, without their ships, to the inevitable when they no longer have a sufficient enough number of ships to keep the population above a critical minimum. I'm not sure if you are being obtuse because you can't admit you were incorrect, or if you really dont understand the implications of that passage. He wasn't talking about the ship population being unsustainable, he was talking about the Quarian population being unsustainable due to loss of ships. I really dont see how you could have misinterpreted that.
Granted, he says their population would decline because their ship numbers would decline. Without correction, this would eventually lead to extinction. One could argue that this would actually take longer than 90 years, and they could obtain more ships or sustain their population for some time at a lower number which would be more sustainable than the previous population size. Still, both the implication of that passage and the context of it imply otherwise. Like I said, read the book if you want the entirety of it.
And the epidemic thing, I didnt feel the need to cite the source on that because the source is Tali from Mass Effect one in classic dialogue that anyone who actually had played the games would know. And those who didnt, again, could easily google. I dont have to hold your hand through everything