Like Arnold told the immigration officer when he arrived on mars (dresssed as a woman in Total Recall) :
Two weeks, two weeks.

Its hard to say how long it would take to fully accept that the person definitely isn't coming back, and be emotionally ready to move on. But, I think it would take me a few years to fully move on to someone else.

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I'd wait as long as it took until that person was marriedto me.

Much longer than his wife did!
In the span of 5 years she lost Chuck, and got remarried and had a kid. All too soon imo.

How long "should" I wait? I don't know. But personally I would probably wait years.

One year tops.

Aww April

maybe 2 or 3 days. Then plenty of fish booty calls

Hence Kelly's conflict. Chuck is the love if her life, but she can't just dump her husband and daughter.
I am a widow and after a long time alone, I recently started dating a nice man. But even if that relationship goes further, my late husband will always be the love of my life, even if I get remarried someday.
It ain't the Ganges, but you go with what you got." ~ Ken Talley, "The Fifth of July"

That's rather cruel and insensitive to your new family.

If I believe there's anything to wait for, then a lifetime. Even if I were to start another family, if that person is the love of my life I'd get divorced once he/she's back.

I think cynic2 is saying they will give up on the idea of the love of their life being found and would start becoming open to the idea of dating once they are emotionally ready

A few months? Ouch will she be left handed or right handed?
Show me the holes!

"no conclusive proof whether s/he is alive or not"
I think you have to differentiate between that and, as in the movie, an
extremely unlikely possibility
that the person is alive. If it were the case you state like if she just disappeared from home or didn't return to her parked car it would be harder to give up, knowing it could be something that case in Ohio, where the brutally insane man kept that woman his sex-slave prisoner for 9 years. But in the case in which she was on a missing airplane, if she were not found quickly I would know it's
virtually impossible
that she is alive especially if it was known there was an explosion [I'm not sure that was known in the movie until Chuck was rescued and interviewed if it was, they should have had a better idea of where it happened, and thus a more accurate search.]
In former case, I'd say 3 years or more. In the latter (like the movie), only a few months.
"Show me the holes!" Is that your signature, or are you trying to add some funny with your question?