If Tesla is using 8000 cells, it is probably putting something like 6-12 cells in parallel packs, and then wiring up each of these packs of cells in series. The parallel cell packs provide the current capacity while the packs in series provide the high voltage required to operate the motors.
If an individual cell in a pack goes bad by having a degraded capacity, the capacity of the pack is degraded. However the pack can keep on operating.
If an individual cell in the pack goes bad by having a dead short a potentially catastrophic failure could occur as current from other cells in the pack flows through the shorted cell. There are probably fuses in the pack to prevent this.
The reaction of the BMS to such events will determine whether the car is dead in water or keeps on operating.
There are, of course, many more failure modes - the wiring harness of the cells could be bad, a bolt could come loose, the BMS electronics could fail and any of them could possibly cause the pack to go dead, till repairs are carried out. The engineers who designed this probably err on the side of safety, shutting everything down to prevent catastrophic failure..
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