User blog comment:B214/Talk About What You Want! 3/@comment-25237578-20141124091015/@comment-1359322-20141124102315

There are many ways of sealing not only one. Rossweisse sealed Loke with multiple seals herself. Azazel sealed Kokabiel in the Cocytus, Koneko sealed Grendel in the BG jewel. The girls sealed the Raygun etc. And all of them only did it once and they didn't have to split their beings/souls into the seals or anything.

And "normally all active magic are gone once the caster dies". Sorry but this is not mentioned in DxD. Also the given reason for God dying is because he exhausted himself after sealing 666 which is reasonable since it's thousands of seals.