So in the future, fiat currency will become digital only and cash will completely disappear. Credit cards will also disappear. People will be implanted with chips that contain all their information and they'll need the chips when buying or selling goods
I have many questions:
How would bitcoin coexist in the future with this method of payment?
Will it get accepted as a second currency?
What about other crypto currencies or bitcoin forks?
credit cards won't disappear they will change form and the future you are describing is not going to happen in many years. and fiat will be in a different form.
and for all we know we all are dead and we shouldn't even be caring about anything by then

but in any case bitcoin will still be different as long as it remains decentralized and alive and with all the characteristics it has today. and any other "digital fiat" will be centralized and that is difference enough for you.