If you read through the link, the estimation for.probability of finding life elsewhere ranges from practically none to very high. When the former is also a.part of that range, could it not be that we actually do not have life anywhere else? I think it's not a question of when or a 'no doubt' case. We simply do not know enough.

If the calculations were to say there's very high chances of the universe teeming with life at many places, but life is not 'found' yet, then I would say it like 'no proof but no doubt'.