Bixby is such a cutie pie!
I would throw out the toy once the plastic bits start coming off 'cuz you don't want your bully to ingest that. Kongs for the most part are pretty tough but there have been occasions when Finn will chew off a piece of the rubber and then I'll throw the whole toy out.
The toys my boys gravitate the most towards are their balls--i got a couple very, very tough ones from @JeannieCO by a company called West Paw. Seems to be chew proof so far! Also, Tate just loves his stuffed Mr.Bill toy. He's gone thru several of these and I do mend their stuffies along the way as long as they're still salvagable. Also, they love their Elk Antlers--very strong, good for their teeth and safe.