I am curious how long the watch will run
No telling, even on a newly assembled rep. I have a few reps now 7 years old still running well with original, unserviced movements. Other reps I received DOA.
When your A7750 fails, you will not likely find any forum watchmakers willing to work on it - they are not repair friendly. But replacement is possible, they are available and not terribly expensive (global economy depending).
If you didn't know, the conventional wisdom is not to operate the chronos at all on an A7750. These movements have been modified (rigged) to mimic the gen subdial placements with cheap parts that can break and leave you with chrono hands stuck in odd places or the movement not working at all. People do run the chronos - if they work, fine but it's a risk you have to evaluate.