Well, I just checked and was able to interact with Leto both with Harah Chani as concubines. Don't know if you tried this yet, but Leto is still in the palace at the same spot as he is normally, he just doesn't have a sprite, so if you click him, you will trigger the event as usual (Try clicking around the red circle on the pic).
View attachment 372402
If you already knew/tried that, then the only explanation that I can think of is that Leto got misplaced somehow (bug maybe?). Sadly, if that's the case, I can't do much about it, I'm afraid. I suppose you'll have to start a new game or try to find Leto. I'm very sorry if that's the case.