Apparently Prigozhin should better have requested to get his amnesty in writing… According to Kommersant and three main news agencies, the case is not closed and still investigated. An unidentified source claimed there had not been enough time to close the case.
In other news (yahoo news, so I would treat it as a rumour at best and don’t want to link it here) it was mentioned, threats to Prigozhins family and the families of his officers stopped the revolt. I find it quite hard to believe, though, that they didn’t see that coming and didn’t take such threats into account.
I don’t think writing would make it any more likely a Russian mafioso would keep to any agreement for longer than five seconds.