Mechanical valves do not degenerate and do not need a replacement because of the duration. Aspirin and Warfarin are life long.
There are no bad effects as long as periodically PT is being done and INR kept around 2.5 to 3.0.
I do not understand what did you mean by emergency bypass also. Valve replacement is always done on cardiopulmonary bypass. If you required an emergency surgery and you are doing well now, results in the long term should remain good.