One of my now dead uncles spent most of his life after Vietnam as a 500-600lb diabetic who gave no fucks about his health until it was far too late to reverse a lot of the damage he'd done to his body.
He lost about 45% of one foot (all the toes and a little of the ball) and everything but the heel of his other foot due to those ulcers that, frankly, if you don't get your shit together and start strictly monitoring your blood sugar, diet, and taking your insulin as well as keeping up with multiple times per day dressing changes and being very careful, will not heal and will just get worse.
My aunt has the same thing; she ended up in a nursing home at 60 because she had diabetic neuropathy, refused to do insulin, refused to fix her diet, and refused to wear shoes despite the fact that she could hardly feel either of her feet. Was constantly getting ulcers and infections that spread and eventually lost one leg from the knee down and got put in a nursing home because her husband, the footless, now riddled with severe arthritis, sure as shit couldn't take care of her.
Basically, that's where Lucas is headed: Stumps and a wheelchair and honestly, he deserves it.
Diabetes in general is not a condition to take lightly, and getting any kind of wound, but especially on the feet or lower legs, is a very serious medical thing. That shit can turn to gangrene and sepsis fast.