I'm almost tempted to just say "f**k it" & predict that Elizabeth will make it to Oct. 19th, 2034 - at which point she'd be 108 years & 181 days old - in order to surpass Sobhuza II as the longest reigning monarch in world history, but even I'd be surprised if she actually made it that long, &
especially so now that her proclaimed "strength & stay" can no longer be there by her side. In any event:
Elizabeth II: 1952-2030
Charles III: 2030-2054
William V: 2054-2088
George VII: 2088-2121
Don't think that Charles will abdicate either, not least because he has waited so long.
I don't think he would want to abdicate but it wouldn't surprise me if there's some exaggerated scandal (maybe something with the Church of England, since Charles isn't too crazy about being Defender of THE Faith, or some meddling in politics) that makes it untenable for him to stay on the throne.
After having waited to reign for so long & - not to mention - having been raised as the son of Elizabeth & everything which that has entailed (i.e., her dedication to duty above all else having been borne directly out of the abdication crisis, etc.), I have to imagine that Charles would only ever abdicate for something along the lines of legitimate health reasons & the like. It's the 21st-century, so we're well past the point of some monarchical church scandal mattering at all, let alone to a significant enough extent that it'd actually result in an abdication. This (obviously) isn't 1936 anymore.
But I don't [think?] the United Kingdom would be at all thrilled at the prospect of a 25 year reign of ol' Charles.
It'll be fine, the British people - when given the opportunity (i.e., in the absence of a church-induced abdication crisis) - seem to always come around to a new monarch sooner or later. I wouldn't be surprised if they probably come to love him as some sort-of 'affable, goofy uncle' for the nation, not unlike Reagan &/or Biden (though obviously without any significant political undertones). Hell, he's practically been primed to be the Edward VII of our times anyway: a prince not exactly known for having great PR, with low expectations for his inevitable reign in abundance after having been blessed with an eternal mother, only to ultimately turn out to have a positive - if not even triumphant - reign.