We hear about it when it happens relatively quickly after the sentence is handed over (Dahmer comes to mind) but sometimes it can take decades and by then media interest has long been waning. And yes, unfortunately, some sickos eventually die of natural causes.
However, child killers always have a contract on their head and it will be carried out at the slightest chance, sometimes during a staged riot, sometimes with the tacit help of prison staff who will allow an "executioner" (usually a gang or mob killer serving LWOP with nothing to lose) access to a segregation area under various pretenses. Sometimes even prisoners who are themselves segregated from gen pop for other reasons, such as snitches or inmates with drug debts, will take it upon themselves to dispatch a child killer in order to redeem themselves. From these there is very little protection.
Even though someone who kills a child killer will be prosecuted his action is viewed as positive by the public and that has to be taken into account during trial, after all he got rid of vermin. More often then not parties will agree on a reduced charge of manslaughter or even invoke self-defense whenever possible. No prosecutor in his/her right mind wants to be perceived as being sympathetic to a murdered convicted child killer and this is an incentive for a would-be executioner to carry out the "sentence" without worry of being convicted of a capital offense.
Today I donated to the fund for Darcy Clarke (mother). She's still in the hospital sedated. God help her!
