Written 7/17/03 and edited 6/27/16; 7/24/16; 8/6/16.
The Greek is οὐδὲ γὰρ ἀποθανεῖν ἔτι δύνανται, ἰσάγγελοι γάρ εἰσιν, καὶ υἱοί εἰσιν θεοῦ τῆς ἀναστάσεως υἱοὶ ὄντες (WH).
This portion of the Lukan verse has, for some time, perplexed me. But I'd rather not get into the aporetic facets of this passage since it would force me to speculate on what Luke might have intended, thus carrying me beyond what the Greek found in the account putatively states.
Suffice to say that angels are evidently not immortal. The only beings that seem to possess immortality (i.e., the quality of deathlessness, indestructibility, and autarchy qua life) are God the Father (Hab. 1:12); the Risen Christ (Rom. 6:9-10; Heb. 7:16) and Christians who participate via divine χάρις in the first resurrection from the dead (1 Cor. 15:53-54). But immortality is never predicated of the angels by any scriptural writer. In fact, some angels actually sinned and apostatized from God, including the one called Devil and Satan (2 Pet. 2:4; Jude 6; Rev. 12:9). These beings now stand on death row, as it were: it thus seems that angels are not inherently immortal.
δύνανται is the present indicative middle/passive 3rd person singular of δύναμαι(can, am able, be capable, have the power to do X). Hence, I like the way that NWT renders the verse. Rotherham also has "For they cannot even die anymore."
However, if these words do apply to those who will live forever on earth, do they necessarily convey the idea that those privileged to dwell eternally on earth will be immortal? Could not Luke simply be professing what the apostle John also prophesies concerning the future inhabitants of the "new earth" in Rev. 21:3-4?
Grammatically, I don't see why we should make a distinction between the individuals mentioned in Lk. 20:34-35 and those mentioned in 20:36. Notice that the Gospel writer employs the Greek postpositive γὰρ, which NWT renders "In fact" (Lk. 20:36):
"Now that" (KJV) "But that" (REV) "But even" (NET)
Luke's use of γὰρ after discussing those who neither marry nor are given in marriage suggests that verse 36 is a continuation of what one finds discussed in 20:34-35. The NWT also evidently construes γὰρ as an emphatic particle by employing the translation, "In fact . . . "
NWT 2013: "In fact, neither can they die anymore, for they are like the angels, and they are God's children by being children of the resurrection."