Not the TV series; the ongoing book series.
George R R Martin is 62. Robert Jordan was 58 when he died. Terry Pratchett is 63 and struggling with Alzheimer's.
GRRM doesn't really have a lot of time left. He took 10 years to write one book (yes, it was split into two but it was meant to be one book). What makes things even worse is that I can't see how he can finish the series in two books.
If you consider the structure of the Wheel of Time, the ending of the series was very clear from the beginning, and it has just become clearer as it goes on: Rand must meet the Dark One on the slopes of Shayol Ghul. Jordan was a master of using prophecy and foreshadowing, so that you knew what was to come, but not exactly how.
Do you have any idea of what the end of A Song of Ice and Fire will be? There's been the strong suggestion that the Others will rise and provide the foe uniting the remaining forces (and Dany + dragons must drive them back), but it seems difficult to see where that could come in the final two books. (And if it's "Others rise, Dragons drive them back" in two chapters, how disappointing!)
If GRRM can do it, I'll be very happy, but AFFC and ADWD have been disappointing from a structual viewpoint, to put it mildly.
Cheers!