Do artists still get paid if you listen to a Instrumental of their song on YouTube?

The easy answer is...unknown.  You see, so many YOutube videos use music without paying the royalty.  If the royalty is paid, then the answer is easier.  The royalty is split up according to the owner of the Copyright, some to the performer, some to the writer.  The amounts differ and it's not really cut and dried.  that's why you should only listen to music you know has paid the royalty, or that you download and pay for from proper places.  

that's up to them.

not all artists care.

The song's writer would get paid, but not the original artist (unless they're one and the same).