The "inactive" (dead) witnesses are those that are no longer running a witness server, basically 'they no longer exist as witnesses'.
As for voting, my stand on that is as follows:
"Every persons vote is a personal choice".
I don't want to be a judge of any persons choices, even those that choose not to vote, even if I don't agree with "non voting" I don't judge people for making that choice.
There is no time limit as to when you can vote for witnesses, so if you are not sure as to who you wish to vote for, take your time.
As long as you understand that your vote is important and does make a huge difference, because each and every person matters in our ecosystem, I am sure that you will take care of it when you are ready to do so.
If you have any further questions, feel free to ask, I will be around.
Cheers.