So one time when I was doing necromancy rituals I had a disconnection. When I came back I saw that the ritual I was doing was canceled. And I checked through my ritual storage box and found that the input item (in this case Greater Necroplasm) was lost. My glyphs also degraded by one point.
I can also confirm that this happens if you leave the ritual site at all. (Happend to me twice, once from chasing a ghostly imp and once from accidently clicking a teleport on my action bar.)
While not an issue for an item like that if you think about it this could happen during greater ensouled cloth rituals. Meaning that if you're unlucky enough for your internet (or jagex's severs) to drop on you then you're going to lose a Subgation part for basically no reason.
I'm unsure if this is due to bad programming or as some sort of way to prevent people from doing the same ritual over and over for randoms. But it should go without saying that this needs to be fixed. It's not likely this will happen to a lot of people but there will definitely be a few unlucky people.
If for some reason jagex is unable to make it remember where you are in the ritual then I would say just have it so that if you disconnect or leave the ritual it will start over without consuming the input or degrading the glyphs. But that ritual will not have any random events.
I am not sure about disconnection but I am pretty sure leaving and returning to the ritual is no problem to me. I made farm runs every 1.5 hours in between rituals the past few days. Nothing lost, nothing degraded.
Given ritual items are probably temporary storage, disconnection followed by certain actions like clearly cache, flush dns explicitly etc may have a chance to lose something.
Ritual focus items are spent & glyph degradation occurs immediately when a ritual is started. Anything that causes an incomplete ritual to be cancelled then means you lose the entire output and of course you don't get the inputs back either.
I've only lost stuff once due to this - chase a zombie impling slightly too far & it cancelled my necroplasm ritual without warning. Disconnecting most likely cancels as well seeing as just leaving the ritual site itself seems to cut it off.
It's more annoying than anything for most as the loss isn't that high, but I admittedly would be pretty pissed off if a greater ensoul ritual got cancelled due to an sudden d/c and i was robbed of a subjugation piece with no greater ensoul cloth from it.