If there's a very real chance that the next shot the enemy will potentially hit on you will make you drop, then just pop it. Popping is better in every way in comparison to being dead, because you'll 1) be alive 2) be ahead on uber by about 25-40% instead of watching the death cam, and 3) you'll be able to keep your teammates healthy in the meantime. If you didn't pop and you lived, yeah that's cool, but you put your team in a horrible position if you drop. If you use, you'll probably lose a control point and then you should sustain at a stalemate.
If you're down by one round and you really need to pull out a solid push with not much time left on the clock, then yeah, I'd do everything you can to hold on to the uber.
A decent amount of the time, you can get around even being in this situation by making sure your team is aware of their surroundings. They need to check for hiding enemies, as well as turning around and helping you out when you're being pressured. Obviously, it doesn't totally rest on your team's shoulders, as you need to make sure your positioning is solid as well.