No, I pretended Jygalagg died some years after due to complications resulting from me constantly destroying his altars, so then suddenly thoere would always need to be a new Jyg, so it constantly cycled through, until finally the cycle was broken by being hurled into the past, (ESO) which would lead to him having many descendants later, who would be the heroes of Arena, Daggerfall, and Morrowind, until the new sheogorath, who is in this way his own great great great great great great great great grandfather, rises up and it starts allll over again. It isn't every hundred years though, it's upwards of thousands of years before the still-mortal Jygalagg dies, it varies.