> wanI'vam lajlu'Qo

I wrote this in order to say "someone refuses to accept this event".

Could I write instead {wanI'vam lajQo' wa'} ? Can the {wa'}, "stand alone" in order to mean "one person/someone" ?

Yes. See TKD 5.2: "Numbers are used as nouns. As such, they may stand alone as subjects or objects or they may modify another noun." But based on TKD, wanI'vam lajQo' wa' probably means one (of them) won't accept this event—in other words, it presupposes the listener already knows about a group, out of which you're singling one. It's not the same as vay' or -lu'.

I think wanI'vam lajlu'Qo' is the superior sentence, and better translated this event won't be accepted.

-- 
SuStel
http://trimboli.name