I assume that it will be clear long enough before that time. If not, then
a) at end of November you can buy a 1-month sub, which will cost you just for the number of days after your then-current subscription runs out, and /or
b) an "until Dec 31st, midnight" option might pop up (pure speculation).
I have no idea if there are talks about prolonging already, or what their status is (if any). So it makes no sense to speculate for me (I'm doing community work and don't know anything about the business side). The only thing I know is that last time (when the first time period ran until end of 2019), it was announced in the middle of the year that it would continue for 2 more years.