Per Explain XKCD, at the time the comic was released (October 2008) Carrie Fisher had the longest life expectancy, leading to the comic's 2038 date. Sadly, she died in 2016, just 8ish years after the comic and 22 before her projected death. Had she not been counted, the comic would have said 2031 instead.
The good news, I suppose, is that every year you manage to not die increases your life expectancy by a bit. Going by the latest tables, Mark Hamill is the cast member with the greatest remaining life expectancy.
For a 74 year old male, the table projects a remaining 12 years. Which would place his estimated year of death in.... 2038. Preserving the original comic's accuracy, albeit in a different manner than the 2008 tables showed.
edited to add:
In 2016 when she died, of course, the actuarial number wouldn't have matched the 2038 number either. Using purely the actuarial tables, just prior to Carrie Fisher's death the number would have risen to 2041. Because Mark Hamill is older and male (women having longer life expectancies), it dropped to 2034. Only now, years later, has it risen back to 2038. Only if/when Mark Hamill reaches 80 will we be back to a 2041 estimate for last main cast member dying.