Yes, I have done any and all of those things for different reasons. When stopped and new build rebiggins,it has sometimes been because of players wanting to try something else or the characters are too busy with life so players want to start a new character. Many times it is because a DM is unwilling to run such a game as one that dares to be over a single level digit. But at last things take shape where the survival and conditions are right and the Hack and Slashers want to try something new or they simplily are not in your game anymore.
It has largely depended on the group and their ablity to play the mechanics in an effecient manner vs. their adversaries on one end and their ablities as players to role play situations on the other. Other than that, it has usually depended on frequency of play.........Most campaigns never see anything above 8th to 12th. Yet, some games go on to Epic level of play.
I don't really have difficulty keeping it challenging at those higher levels of play although characters are fairly easy to kill off at lower levels of play. So, much easier that "accidents" can kill all the original party members off in a few sessions if the players or characters are not catching on to even a simple trap.......If someone dies and can not report what has taken place I see no reason to reveal it completely, the method of death without full disclosure is often best.
Higher levels of play do have different approaches to many things yet it is every bit as playable and allows for many different settling in of responsiblity demands upon the characters as they learn that being responsible for a small successful adventuring band was only the beginning of their troubles and was in fact far easier and simpler before their success and enlightenments.
Basically the old addage of "With great power comes great responsiblity" & "To whom much is given much is required" comes into play full blast and the DMs job changes yet is often even more fun as being a nuisance and informer of "issues" becomes a mostly role playing issue and less to do with mechanics until things really warm up!
Fun times all round. Retirement? If characters are still alive after being blessed with a life, that hasn't ended, to give them position in a world; then they could be so lucky......Time to show them why being a nobody was easy! zzzzzzzzzing. Ha!
I could give details on how recording sessions can haunt players later when you start doing to them what they have been doing to other High ups! HA
I have had my own DMs do the same to me........and I enjoyed every bit of it on both sides of the gaming table.
The mixed levels keeps things interesting and honestly more realistic.
I say,"If they endure, keep the campaign alive long enough to become a burden to your players!".......If you do that well they will love you for it!
HGF