The Sphere of Annihilation (of the party)

Hello all,

I have been running a level 20 epic campaign where the party is trying to defeat a lich who has ruled over a land full of monsters for hundreds of years blah blah blah etc etc. Anyways to make things fun as they have been hunting for the lich's phylactery I also chose to send the Grim Reaper after them since we are using Pathfinder 2e and he has a stat block in that game.

So they eventually discovered a Sphere of Annihilation that I put in the game cause it seemed like fun and the players got an idea. They got a wonderful, terrible idea.

The Grim Reaper followed them to this sphere, then they ambushed him and managed to shift the Sphere over to him and annihilated him utterly. Unfortunately they also destroyed themselves in the process. It is a party of seven and four of them were fully annihilated, two are out of range and have survived, and one has attempted to use dimensional anchor on themselves and is hoping that in my benevolence I will allow him to survive. He is also the one who killed everyone by moving the Sphere in the first place.

Does anybody have any ideas on what to do now? While we are all fine with the party dying, I would like to reward them for this incredibly creative solution not punish them. We are also so close to facing the lich himself as they had just managed to destroy the phylactery, so I would like to finish the game. Should I have some god save them but at a cost? Maybe the one is tethered finds some way to pull the party out of the Sphere while the players in the Sphere fight the Grim Reaper on the edge of the Abyss or something? Happy to hear suggestions for fun ideas. Anything goes cause they are level 20 and we are a wacky bunch already.