I wish they had explored more God tier death mechanisms in Homestuck. I don't think anything about obstruction of healing was covered, so bear with me: Dave preventing Dirk's corpse from healing so that he can interact with the body for longer. Just decapitating Dirk and then covering the stump of his neck with plastic wrap or something so his head can't rejoin.
Dave getting to record a video of him keeping his cock shoved down the wrong end of Dirk's throat and holding it there so he can show Dirk the video later and see if Dirk has any opinions on if that's Dirk warming Dave's cock or if that's Dave warming Dirk's head. Dave getting to just really have fun with Dirk's body, having all the time in the world to mess around with how limp and loose his body is. He can do any position, so long as he can find a way to haul Dirk's body into it and hold it there even while he's just dead weight (literally).
It doesn't even have to be sexual, just Dave setting up a camera to record a whole hour of himself cuddling with Dirk's corpse on the couch, of holding Dirk's body like it's just an object, of contorting Dirk's body in ways that would probably be very uncomfortable if not painful so that Dave can get more comfortable while lying down with it. Dirk would enjoy watching that video, even in a nonsexual way I think he would enjoy just being used as an object for the happiness of people he cares about, and the way that Dave just does whatever makes himself happiest while Dirk is dead makes Dirk feel satisfied in a way he doesn't even get while he's alive and being cuddled. A corpse can't complain about a position, a corpse can't even make a pained little noise if Dave starts squeezing its ribs a little too hard. A corpse can't bother someone by being too needy or being uncomfortable. It's also something about the way that even when given the option of doing anything to Dirk's body, Dave still chooses to just snuggle in. Dave wants to cuddle with Dirk, just as much as Dirk wants to cuddle with Dave, and since Dirk can't say or do anything to convince Dave one way or another, that means that that desire from Dave must be genuine.
I don't think the body would decompose, since it's still "alive" in the capacity that it can be brought back. Theoretically, Dave could just keep Dirk as a corpse for days, weeks, months, hell even years if he felt like it. That sort of implicit trust is something that Dave really values, the fact that Dirk is handing over his own existence and letting Dave fully control when Dirk is allowed to be alive. If Dave made the decision to keep Dirk dead for decades, Dirk would have no way of objecting, or even of knowing that it was happening until after he comes back to life. Dave doesn't really abuse this though, he still needs a lot of attention and while Dirk's corpse can be fun to mess with, Dirk's corpse cannot tell Dave good morning and good night and obsess over if Dave is eating enough and drinking enough and make Dave feel like he's being seen right through in that humiliatingly vulnerable way that Dirk himself can.
Completely opposite everything in the post but I don't want to hide this in the tags: it's fascinating to think about it in the other way too, where Dirk's body will be brought back, even if he'll just experience pain and then death again. Dave attempting to put plastic wrap on Dirk's neck stump to stall his revival, only to find out that no, God tiered characters cannot stay dead if it wasn't Just or Heroic. Dirk coming to with the edges of plastic wrap sticking out of the skin of his neck; with his veins and muscles and nerves only connected enough to keep him feeling every second, keep his brain functioning, and allow movement of his neck; with the full sensation of his airway being obstructed by plastic wrap that's taut across his throat like the skin of a drum, making horrible sounds as he tries to desperately suck in a breath of air. Dave watches in horror as Dirk claws at his throat for a couple of minutes before dying again, only to revive a minute or two later and experience the exact same thing. Eventually Dave has to step in, he has to decapitate Dirk again and put in a lot of time and effort pulling out the freshly enervated plastic wrap from Dirks muscles, since Dave can't quite get the decapitation on the right line to take the plastic wrap off the normal way now. Dave definitely can't get all of the pieces out the first time, so he has to decapitate Dirk a few times and practically shred Dirk's neck each time to get all of the scraps out. I think it's the sort of event that would really change Dirk's brain chemistry. The idea of Dave doing that again but just making Dirk sit through days of that agony before stopping it will not leave Dirk's head. Dave is too freaked out from that to even do their normal necro stuff though, so Dirk keeps his mouth shut and instead stews in guilt for enjoying something that upset Dave so badly.