...לְכַלּ֥וֹת אֶת־עֵינֶ֖יךָ וְלַאֲדִ֣יב אֶת־נַפְשֶׁ֑ךָ וְכׇל־מַרְבִּ֥ית בֵּיתְךָ֖ יָמ֥וּתוּ אֲנָשִֽׁים׃
…to make your eyes pine and your spirit languish, all the increase in your house shall die en masse.
(The above rendering is the footnoted alternative rendering in the RJPS translation, an adaptation of the NJPS translation. Before accounting for this rendering, I will analyze the plain sense of the Hebrew term containing אִישׁ — or in this case, its plural אֲנָשִׁים.)
Now, it is indeed rare for אֲנָשִׁים to be used adverbially in predication. Prototypically, this plural form of the situating noun indicates a group’s definitive participation as such within a depicted situation. Accordingly, in the present predicate, אֲנָשִׁים straightforwardly describes the death scene by evoking a multiplicity of simultaneous participants in the event: “die as a group.” As such, this prediction foretells (or at least foreshadows) the mass execution of Eli’s priestly descendants that will be recounted in 22:18–20. This construal readily yields a coherent and informative text.
Interpretation of the cryptic expression יָמוּתוּ אֲנָשִׁים is hindered because it appears within a verse whose meaning is uncertain (and whose text is also uncertain, given the Septuagint’s evident divergence).
As for rendering into English, the NJPS ‘as [ordinary] men’ is a guess for a longstanding interpretive crux. Unfortunately, the NJPS construal does not yield an informative text. The revised rendering, borrowed from French (and placed in a new footnote), is the most idiomatic way of expressing the adverbial force of אֲנָשִׁים in English.