According to this article in the Rocky Mountain News, McCarrick's resignation isn't even official yet (meaning he could still chose to stay on a few more years). Please tell me this reporter is wrong.
Each Bishop must submit a letter of resignation on his 75th birthday. In the past, these have largely been ignored for up to several years. Since Pope Benedict has just started his Pontificate, and since he has not even reorganized the Curia, it is widely suspected he WILL accept these routine pro forma resignations to begin to get his own prelates in place. One of the first major ones coming up is July 7th with Cardinal McCarrick who heads a very visible Diocese and who had a "run in" with the Prefect of the CDF.
The Vaticanisti blog stated that his resignation WOULD be accepted. This is the same group that stated Archbishop Levada would head CDF when many thought they were daft so their batting average is 100% in their first major test. We can only wait to see.
Frank
It's only his choice to remain if the Holy Father does not accept his resignation. All must submit their resignations at age 75.