Sounds like a good luck story.
But as to your original posting. .. while a battery pack is in theory repairable , one has to examine the cost benefits in doing so. .. while finally only 1 or 2 cells have faulted, the remainder will be quite old and worn. To identify the defectives means braking into the pack which is welded together , and extracting them, then replacing them and rebuilding the pack and rewelding. The action of welding puts stress on the cells.
Once done, what reliability has the new pack, considering that the majority of cells are old?
What repairer could give any guarantee?
There is a lot of labour in the task, .. it's not like demolition it's more like reclaimation. And unlike new battery pack manufacturing, there isn't the economy of scale or the use of jigs and fixtures.