Good question. I would wait until after the services for the deceased, maybe 2-3 weeks, unless it is an emergency. It's still a professional situation, so if you need medical assistance for ANY reason make sure to go in.
I'm not so sure of your question; do you mean when should a patient of the doctor who died, expect that the office has made arrangements for a replacement?
If that's what you mean, like the other poster said, if what ails you can wait until after the services, I'd wait. But, if you have an urgent need, you're well within your rights to expect that there is a replacement doc available NOW. He/she may not be the permanent replacement, but if you need treatment, you need treatment and should seek it.