A guardianship or conservatorship of an incapacitated adult will probably last as long as she lives. It could be ended, however, if she regains the ability to make decisions. A financial conservatorship might be ended if she no longer has any assets to deal with.
Although the guardianship or conservatorship itself will probably continue as long as your family member lives, the person serving as guardian or conservator might change. This could happen if the guardian or conservator dies, moves away, or otherwise can no longer serve in such capacity. A judge could also replace the guardian or conservator with someone else if they repeatedly make poor decisions or neglects his duties. A family member or any other interested person could request a change by filing papers with the court detailing the reasons the guardian or conservator should be replaced.