Probably not a good translation. mauya sen pene probably means 'he/she must be lacking', but to lack something does not necessarily mean to be in want of something, to need something. So maybe simply mauya sen ma 'he/she needs something', but then it is missing the 'must be, surely' part.

Rather ildome, maybe?

I wonder if *ilse would be a form Tolkien would've come up with.

Could *ilyave be used for 'universally'?

 Isn't erya for 'not married' too much of an anglicism?

+Björn Fromén perhaps it is. In Hungarian we say egyedülálló "standing alone"

+Tamas Ferencz What's wrong with pure analytical *alberna?

+Александр Запрягаев
nothing. You're asking as if I'd deliberately cast it aside as a possibility:)

+Tamas Ferencz
It's the same in Swedish: ensam-stående 'alone-standing'.

+Björn Fromén
so if artarindo and astarmo mean 'bystander, witness', could *ertarmo mean 'bachelor'?:)

+Tamas Ferencz
Possibly, but also 'hermit', 'recluse'. A less ambiguous word for 'bachelor' would be *alvestano or *alvertano (modelled on nehtano).

+Tamas Ferencz Well, having root BER and refusing to use it seemed like that to me) Unless you use a specific 'bachelor' word, and unmarried person is marked in Russian as it is, 'un-married', al-verna (albériéla?).

+Александр Запрягаев
sure, there are several possibilities. Unmarried is certainly one of them.