Is the Pit from a Robe of Useful Items permanent and can it be dispelled?

If you place the Pit from the Robe of Useful Items, will it remain there forever, as if it was dug? RAW, I assume so. The RAW on the Robe of Useful Items doesn’t say anything about the items being temporary, so we should assume they are not.

I’m less convinced on Dispel Magic, and I know I will have to make a ruling on this, likely in a session or two, but I am leaning toward no. If the patch has "become the object or creature", then this is a normal, everyday, non-magical pit. The magic was in it’s creation, not it’s essence. As such, dispel magic would have no effect, right?

Or am I perhaps overlooking something?