This refers to Matthew 17, the transfiguration. So the Word from Christ is indeed fulfilled.
Edit: My apologies for being too brief.
Matthew 17 and the scripture you quoted, Mark 9, both reveal the answer to Christ's words. The sight of God's kingdom was the Transfiguration, the disciples present saw Elijah and Moses, who are in heaven, momentarily, and then heard the voice of God speak, which caused them to fall on their faces.
To address the second point, I'd look at 1 Corinthians 7:6-7 where Paul instructs people to marry if they so please, or to stay unmarried.
6 But I say this as a concession, not as a commandment. 7 For I wish
that all men were even as I myself. But each one has his own gift from
God, one in this manner and another in that.
8 But I say to the unmarried and to the widows: It is good for them if
they remain even as I am; 9 but if they cannot exercise self-control,
let them marry. For it is better to marry than to burn with passion.
The twinkling of an eye passage I think you are referring to is 1 Corinthians 15:51-52.
51 Behold, I tell you a mystery: We shall not all sleep, but we shall
all be changed— 52 in a moment, in the twinkling of an eye, at the
last trumpet. For the trumpet will sound, and the dead will be raised
incorruptible, and we shall be changed.
This is referring to Rapture, where we do not die but instead are changed; this is often referred to the spiritual body in non-denom Christianity, and it occurs in the last days.
Hopefully this is more helpful than my original answer!