τοῦ ἀποθανόντος περὶ ἡμῶν ἵνα εἴτε γρηγορῶμεν εἴτε καθεύδωμεν ἅμα σὺν αὐτῷ ζήσωμεν. (1 Thessalonians 5:10)
BAGD and Thayer understand Paul to be discussing literal death in 1 Thess. 5:10. Additionally, Ralph Earle writes:
"The verb GRHGOREW means 'to be awake,' as well as 'watch.' In view of the previous part of the verse--'Therefore let us not sleep, as do others'--it seems evident that the best translation here [in v. 6] is 'keep awake' (RSV). The same verb is translated 'wake' in verse 10, where it means 'alive,' not sleeping in death" (Earle, ,372).
So it appears that Earle understands καθεύδω in v. 10 to denote the literal death condition of those in Christ.
David J. Williams also insists: "It is inconceivable that Paul should suggest that whether we are morally alert or moribund will make no difference in the end. KAQEUDO is here synonymous with KOIMAW in 4:13ff (for this sense of KAQEUDW as physcial death, cf. Mark 5:39; also LXX Ps. 87:6; Dan. 12:2; for similar statements concerning Christ's death and its outcome, see Rom. 14:8f; 2 Cor. 5:15, 21; Gal. 1:4; 2:20). Paul ends as he began the section by assuring the Thessalonians that in whatever their physical condition at the Parousia, whether dead or alive, they will not be disadvantaged" (Williams 91).
We also have these comments from Henry Alford:
who died for us, that whether we wake or sleep (in what sense? surely not in an ethical sense, as above: for they who sleep will be overtaken by Him as a thief, and His day will be to them darkness, not light. If not in an ethical sense, it must be in that of living or dying, and the sense as Romans 14:8. (For we cannot adopt the trifling sense given by Whitby, al.,—‘whether He come in the night, and so find us taking our natural rest, or in the day when we are waking.’) Thus understood however, it will be at the sacrifice of perspicuity, seeing that γρηγορεῖν and καθεύδειν have been used ethically throughout the passage. If we wish to preserve the uniformity of metaphor, we may (though I am not satisfied with this) interpret in this sense: that our Lord died for us, that whether we watch (are of the number of the watchful, i.e. already Christians) or sleep (are of the number of the sleeping, i.e. unconverted) we should live, &c. Thus it would = ‘who died that all men might be saved:’ who came, not to call the righteous only, but sinners to life. There is to this interpretation the great objection that it confounds with the λοιποί, the ἡμᾶς who are definitely spoken of as set by God not to wrath but to περιποίησιν σωτηρίας. So that the sense live or die, must, I think, be accepted, and the want of perspicuity with it. The construction of a subjunctive with εἴτε … εἴτε is not classical: an optative is found in such cases, e.g. Xen. Anab. ii. 1. 14, καὶ εἴτε ἄλλο τι θέλοι χρῆσθαι εἴτʼ ἐπʼ Αἴγυπτον στρατεύειν.… See Winer, edn. 6, § 41, p. 263, Moulton’s Engl. transl. 368, note 2.
ἅμα] all together: not to be taken with σύν, see reff.
For another viewpoint, see M. Lautenschlage in ZNW 81 (1-2, 1990), pp. 39-59.