The extents of Gremmy’s power are never really discussed, and I think his character was just poorly written in general. Nevertheless, for all his incredible and very overpowered abilities, he is still a minor villain who meets his end at the hands of Kenpachi — who wins simply because he is really, really strong. Gremmy’s body is unable enough to hold Kenpachi’s power, and it disintegrates. All that is left is his brain in a class case; however, the only reason he actually dies is because his imagination “reached its limit”, whatever that means. His artificially created body was certainly destroyed like all his other creations, but there’s no indications at all that his mind was also broken, so I don’t see why he couldn’t just create another form for himself and escape somewhere else.
As this battle concludes, another one quickly shapes up with the arrival of Bambietta’s crew, minus Bambietta. I assume they absorbed her power after her defeat, and like Yhwach, their comrades’ deaths only make them stronger. Even with the boost though, it doesn’t seem likely that they will stand a chance against even an injured Kenpachi. Also, if Bleach follows the usual formulas, characters generally don’t fight multiple opponents at once unless they are destroying them in one shot (e.g. Ichigo, Kenpachi, Aizen), so I’m guessing Kenpachi will leave this fight to several of the lieutenants who will face the girls individually as he goes to search for the missing Yachiru. There are still several unexplained aspects of Kenpachi and Yachiru that were hinted at in the previous battle, and I feel that something strange may have happened to Yachiru. No doubt Kenpachi will stop at nothing to get her back, and we are yet to see the full fury of his power.