Allegedly. There’s no evidence to back this claim other than the guards were on break when he died. If I were to plan my demise in jail, I’d wait for the guards to go on break as well. Less chance of them finding you before you’re gone.
His client list is quite well known. So far as I know, and in spite of the evidence, no one on it has ever been questioned - apart from Prince Andrew, and that was the result of a civil case.
With Epstein dead there's no reason why anyone would be. Any former "party friends" can always be paid off, or discouraged in less subtle ways.
The more interesting question is - who replaced Epstein?