A Biometric card has an expiry date just like a debit card. That does NOT mean you will lose your settled immigration status, similarly when your debit card expires your bank account does not disappear
You simply need to apply for a new card, your status as settled resident will not change. You can even enter the UK with an expired ILR biometric card.
Disadvantages of staying on ILR (instead of becoming British) is that you could lose the settled status, for example if you are absent from the UK for more than two years or commit a serious crime.
Advice is given based on my personal research and experience only. Do NOT contact me via private message for immigration advice