Can I trust anyone? Can I trust that a particular person will not drink, will remain in recovery, will get well?
To trust someone means to be certain that they will act in a particular way, specifically that they will act well.
No one acts well all the time. In that sense, no one can be trusted. What we're really talking about is the likelihood that someone will act well. No one is trustworthy but some people are more likely to act well than others. Even then, people surprise us, in both directions.
Furthermore, sight of the future is reserved for God. To predict the future, for good or for ill, is to usurp God's role. I don't do it. When people ask if I'm looking forward to something, I say I do not look forward. Above my pay grade. Also impossible: nothing is as it is predicted to be. One casts one eye into the future in order to plan right action and take reasonable precautions, but holding one's nose at all times, lest one acquire a taste for the the tempting incense of the soothsayer. Having gleaned what I can, I return to the present.
Where does that leave me and the alcoholic? Well, no one can be trusted to stay sober, stay in AA, stay well, stay humble. Practically speaking, one must act as though one trusts people, e.g. making plans with them, relating personal information, asking them to do things (and assuming they will do them), but it must always be with the equanimous realisation they may fail.
Specifically regarding alcoholics in recovery: someone who has completed the first nine steps, with no active addiction, no grumbling resentments, no unfinished amends, who has an active spiritual life and helps others constantly is largely secure right now, but even that is conditional only on the maintenance of this condition.
At the end of the day, only God can be trusted. To trust a person faithfully is to treat the other person as God. So I trust God instead, and let people come and go.