Hi.
Last summer AZ saw some crazy high temps. I used a shade cloth on my new Mexican Fence Post because it was scorched (see picture). It grew a couple of inches and poked right through the shade cloth… scorching the top of the post (see second picture).
Now I have six beautiful pups growing from the tippy top!!!!!

It will be interesting to see what happens with this. I'm worried it will get super top heavy. It's also near corner of house with lots of foot traffic.
Thoughts on what this will grow into? I have images of a mini saguaro.

Or what I should do?
I'm intrigued to leave it alone and see what kind of mutant I end up with.
Should I propagate pups off? If so how big should they be before I try?
Help!

If you damage a normal cactus' growth center(apex) it will start branching. The same way you get stem cuttings from most columnar cacti. I think the same should apply to euphorbias. Now I do say normal cacti- by that I mean the bulk of the species and genera are either columnar, or columnar-epiphytic(hylocereus), or short columnar(echinopsis). Id wait a while(a few months) and start these as cuttings, seeing as the original stem will never recover and decline slowly. Id say either frost bite or very severe sunburn...
We even had a thread/discussion where some members use a drill to "core" several types of barrel cacti to produce pups. The outcome is pretty much similar to yours.

This is nature's gift to you after the plant lost its growth point. Put a cactus on the brink of death and sometimes it comes roaring back as if to say I'm still alive! Stefan has summarized the situation nicely.

You might need to protect the new growth from hot summer sun. Try to avoid repeating history there as you might not be so lucky next time.

Your ability to start new plants from cuttings is partly dictated by their starting size, partly dictated by the season. So maybe in the fall when it's not so hot, or maybe early next spring to gain a size advantage. But not during the extreme heat of summer or the colder days of winter.

Rootless cuttings will benefit from some sun protection (ideally shade cloth or morning sun only, no overhead sun during the brighter/hotter months). Only after they are properly rooted and growing (maybe 6 months or a year after being started) can you safely consider giving them a more exposed location.

We can give detailed instructions on starting this cactus from a cutting, but I think it is best to wait before doing so.