M,
I have found that windows will eventually kill the process. It can take three or four minutes though. Restarting may be faster but I find that even shutting down can take several minutes because (I think) Windows is waiting for the process to end. Have you tried just restarting Cubase with the old Cubase process still running? I have done this a lot of times and as long as the ASIO driver was released, I have been able to continue using Cubase with no problems. Then, after I am done, I sometimes check the task manager and see that the old Cubase process did eventually end.