Undelete a deleted object

I don't think a 'deleted' object can be restored (unlike a 'disabled' object).

From https://en.uesp.net/wiki/Skyrim_talk:Console/Archive_4#Undo_Markfordelete.3F:

There is no way to create a reversal for the markfordelete command that I have found in my research. I have not found a way to reverse this command once it is entered as it creates a permanent flag on the item to never render it or allow scripts to run for/including it, and it does not seem to be a toggle type command that can be turned on or off. The best way to think of the console is that it is the "master script" for the game that you are live editing when you enter a command: that is why all of the warnings on using the console for anything. This is no help to you, I know: I hope it is a warning to others though

A thread in the Skyrim Steam forum seems to suggest the same thing. In the same thread, though, a user suggested to use the resetinterior console command (resets an entire cell) while outside the cell, to try the restore the deleted object in the cell. I'm not sure if this will have negative effects (although I assume it will).

What, I think, is missing from the existing answer is an explanation for the missing Rundi. This/he is part of the quest: The Missing Apprentices.

This quest.... does not exist. It is one of several items of cut content from Skyrim.

However, several mods are available which restore this content, the best known is The Cutting Room Floor by Arthmoor.

This mod is available, of course, on Nexus for Skyrim, on Nexus for SSE, but is also available for the XBox One.

The Cutting Room Floor is, sadly, not available for the PS4, however there is another mod available for the PS4 that restores this content which is called Skyrim Restored by Salvadorc17.