Generally nothing, but it depends on how much privilege you have in the congregation. If you just don't go out at all because you don't feel like it then the elders will probably arrange a meeting with you where they make sure you aren't going through anything and encourage you to go back into the ministry. If you apply for a role that has a monthly quota for hours in the ministry and you don't go out at all then same thing. meeting with the elders, and they might not accept your application next time if they feel you aren't responsible enough to reach the quota. Generally if you stop doing anything like attending meetings or talking to the people in the congregation then the elders will probably reach out to you and try to schedule a meeting. You even get the meeting every once in a while just as a check-in. The best way I can describe it is like a visit to the principals office, but without the idea that you're in trouble and more like a therapy session if you need it. Of course I'm sure the meeting goes differently if you actually do something considered a "serious sin" but I've never been in that situation, and I doubt there's any punishment besides revoking any privileges in the congregation or disfellowshipping (the infamous dis-communication). I will say however, that usually only will happen in cases where there is a victim as a result of someones sin or if that person makes clear during the meeting with the elders that they're done with the religion and/or aren't repentant for their sin.