Infection, pain. If you've had kidney stones for a long time, several things can occur. It can cause no symptoms at all or you can develop symptoms at some point. Problems inlcude bloody urine, kidney damage if there is blockage, pain in the kidney area, or recurrent urinary tract infections.
Depends. Tiny asymptomatic stones often cause no chronic issues. Large or grownign stones, especially when associated with infection, can cause serious blood infections, renal function loss, and / or renal tumors (squamous cell carcinoma of the renal pelvis). Again, tiny stones that are stable will not produce chronic or deteriorative issues.