Hittite law, as most ancient law, was pretty strict in the beginning. The death penalty for pretty much everything strict.

As time progressed the laws became progressively less severe. Instead of lethal penalties, fines and reconstitution were used more and more for law violations. Compared to say Babylonian law they became relatively liberal as time went on.

A rather large proportion of the laws deal with sexual offenses. They also leave us wondering. For example, bestiality was punishable by death even in the more lenient period, BUT an exception was made for sex with mules and horses.

"Speculation on why one may have sex with such animals but none others has led to a number of explanation in the scholarly literature which are ultimately inconclusive, even if they have the merit of being ingenious and entertaining"[1]

By this point in time you would get the death penalty for intercourse with a sheep but a fine for the murder of a man.

The crucial point here is religion. If a man becomes unclean by bestiality he risks polluting his entire community and bringing down the wrath of the gods on his neighbours. A case in point, anything, however trivial or accidental, which might pollute the king of a priest would likely be a capital offense as it would but the entire nation at risk of the wrath of the gods. Even normal sex would make a man unclean requiring bathing before he could pray.

The laws of the Hittites (what we have recovered) were not exhaustive. For many 'normal' offenses we have not found laws. This does not mean there were none. They might simply not have been written down or have been handled locally by the village council or something like that.

As such I really doubt that the Hittites would condone necrophilia as I can't recall ever reading anything like that. Not like it didn't happen in the ancient world. Herodotus speaks of Egyptian relatives waiting to deliver a dead beautiful girl to the priests for burial until decomposition had started as they feared the priests would violate her corpse.

[1] Life and society in the Hittite world, Trevor Bryce (chapter 2 The people and the Law)

As a side question, is there evidence of how commonplace necrophilia was in hittite realms? Was it ritual in nature or solely sexual?