The expression “standing before the throne” does not necessarily always mean that the one is literally in heaven before Jehovah. For example, Jesus warned his followers to “Keep awake, then, all the time making supplication that you may succeed in escaping all these things that are destined to occur, and in standing before the Son of man.”
The Son of man, of course, is in heaven, but his disciples on earth are spoken of as standing before him. In what sense? When God judges people they are spoken of as standing before him. So, those who keep standing before the Son of man are those who will receive a favorable judgment. Elsewhere, the Bible states that the wicked will not stand up in the judgment. That means they will receive an adverse judgment.
The fact that the great crowd is spoken of as standing before the throne and also coming out of the great tribulation, means that they survive the tribulation and receive a favorable judgment.
The 21st chapter of Revelation makes it very clear that people are going to survive the end of the world, because it states that in the aftermath of the judgment God will be with mankind and they will be his peoples.