User blog comment:B214/Volume 23 discussion blog/@comment-190.160.185.214-20170325175848/@comment-10330822-20170325185105

I suspect Volume 30 is a epilogue volume too. Or at the very least, part of the volume will be epilogue. I can't see this series ending with Sirzechs and company still stuck inside fighting Trihexa. My guess is that last volume will be set after the EX story and will have Issei and his friends free Sirzechs and the others and finally destroy Trihexa.

Volume 29 may be Issei and Vali's final battle, but it also may be the start of the UL interdimenaional war.