1) Bitcoin becomes too expensive to mine or even sustain due to energy prices

2) Bitcoin's blockchain grows to petabytes or exabytes in size thus becoming horrendously slow to both replicate or even host

3) Bitcoin is surpassed by a better technology, such as Cardano or IOTA. This won't kill it but it will stunt/cap its growth indefinitely.

4) Bitcoin fails to integrate into the legacy world fully by remaining pseudonymous, reluctant or refusing to comply with AML/KYC regulations everywhere in the world, developed or not. It then maxes out in growth. Again, not a failure case, as whatever value was there will probably still remain, but it will be dwindled down significantly.

I'm sure there's more but I can't think of all of them...