What I've of seen few people do who left the Borg is just show up for the wedding ceremony at the Kingdom Hall, congratulate the couple and maybe pass on a card with a gift certificate.
Realistically the JWS are trained to demean people who left the JWOrg., they are identified as not to associate, evil, unfaithful, unrighteous etc. by the Borg leaders so from that instruction people will act in various ways.
What I've seen in social engagements with JWS and elders people there they will act further toward that instruction, perhaps even more so.
Some will give you a cold shoulder, some will be actually happy to see you and will talk greet without being judgemental.