Group critical illness benefits through work typically max out between $10,000 and $30,000. The average first-year out-of-pocket cost of a serious diagnosis is 3–5× that. The group policy also usually ends the day employment ends - which is often the exact moment the diagnosis forces someone to stop working.
The stack that works
Keep the group benefit. It's cheap and it's real money. Then own a personal policy on top of it that (a) is portable, (b) has level premiums, and (c) is sized to cover 6–12 months of household essentials. That combination is what actually keeps families out of medical debt.