If a user is frequently downvoted and falls below 25 rep, the requirement for posting example questions and the lowest privilege, how can he or she re-earn that privilege?
Time, reputation (up or down) tends to fall away as proposals are deleted. Deleting a poorly received question will also remove lost reputation.
On Area 51 it does not always happen in real time. Periodically reputation is recalculated. One day you have some rep the next day 30% is gone.
Manual recalculations can be initiated by moderators. If you lost a bunch of rep on down voted questions, delete them. If you don't get it back in a day or two, ask a moderator to recalculate your reputation. Be aware manual recalculations may have unanticipated results
Several related posts can be found here