Russia demands to see the Skripals, so that they have the chance to get consular help if they want it.

Even though it is possible that Russia poisoned them, I think the UK should uphold this right. It often comes to the aid of prisoners, and if the UK disregards it, that will encourage other countries to do the same.

If they do not become able to communicate, they are very likely effectively dead. Or else they are conscious but locked in, which could be a fate worse than death.