Here "pass away" is a polite way of saying "die." AT: "this generation will not all die" (See: [[rc://en/ta/man/translate/figs-euphemism]])
# this generation
Possible interpretations are 1) "all people alive today," referring to the people alive when Jesus was speaking, or 2) "all people alive when these things I have just told you about happen." Try to translate so that both interpretations are possible.
The words "heaven" and "earth" are a synecdoche that includes everything that God has created, especially those things that seem permanent. Jesus is saying that his word, unlike these things, is permanent. AT: "Even heaven and the earth will pass away" (See: [[rc://en/ta/man/translate/figs-synecdoche]])