Cook sausage on an outdoor grill or grill pan over medium-high heat for about 3 minutes per side.
While sausage is cooking, heat canola oil in a large skillet over medium-high heat. Add cabbage, onion, garlic, red pepper flakes, salt and pepper. Cook, stirring often, until the cabbage has wilted slightly, about 4 minutes.
Add apples, beer, vinegar, mustard, brown sugar and sage. Stir until incorporated; bring to a simmer for 5 minutes. Add sausage to cabbage mixture, cover partially with lid to allow some steam to escape.
Reduce heat to medium-low and cook until cabbage and apples are tender, about 8 minutes. Serve as-is or on grinder rolls.