On the other hand, there is nothing stating that creatures lose spell-like abilities as they lose HD either. Only a few creatures gain Sp abilities as they advance, but those are very specific cases. Most simply advance HD and gain no new abilities, hinting that the opposite, losing HD, would also not lose any abilities.
If you Sirmiculum a Githyanki, the copy could easily be argued to lose spell-like abilities because Githyanki DO gain more abilities as they advance. If you do the same to a Malrith, things become far more questionable, since they gain no new abilities as they advance in HD.