Mmm, Leannes cult thing is going to fleece her for all Nicks money and something will go tits up and THEN it will dawn on her. Or somehow Sam will get mixed up in it...which will press all of Nicks buttons at once and his head will come right off.
You can be charged with murder and convicted of it, without a body.. but..
You would need significant forensic evidence to prove that the person could not be alive - in the case of blood you would need proof that there had been so much blood loss that the person couldn't survive. Now I know that a small amount of blood does go a long way, but the amount needed for certain death would involve a huge LAKE of it on the floor, which there was not. Or to get it up the walls, arterial spray (which would be high, wide sprays/jets of blood).
We saw a small amount of blood on the curtain and wall behind the curtain, that could fit with someone facing the wall, on their knees having a rather oddly positioned nose bleed (or a set designer pouring something down the curtain and wall!)...
Absolutely no way could Roy have missed that amount of blood or mistaken it for anything else, it would have really ponged as well!
Unless there is evidence viewers were not shown, there is no way this would be enough to charge with murder. As well as the not enough blood issue, theres no indication how anyone got a body out (no blood droplets transferred, no drag or streak marks). Which suggests she walked out rather than was dragged or carried out.
Of course you can kill someone and NOT have them leak everywhere - but thats their entire argument, that there WAS enough blood for Lauren to be dead. If they were arguing she did not lose sufficient blood to die.. then whats their proof she is dead?
Roy has good reason to have cleaned the flat. The evidence he was there is consistent with cleaning the flat for Evelyn. They really have nothing.