Had a spirited downhill ride of about 10km of 30kph bends and coming to the end have no rear brake left, boiled the fluid. Five minute rest and all is good again, should I replace the fluid as a precaution?

yes... it's boiled once so there is probably moisture in it

+1 on that brother

You use the rear brake that much? Sometimes I'll use mine during spirited mountain assaults as a means of traction control and speed control to a small degree, so it's engaged to some degree for nearly 10 miles straight, but never had any fade. In addition to a good purge I would give the caliper and pistons a good scrubbing. And while you're back there give the disc a light buffing with emory cloth or fine grit sandpaper to remove any glazing or embedded pad particles.

Yes change the fluid.
You should change your fluid annually or when you notice it has changed color.

How old is this brake fluid of yours? Not that important - as others suggest, replace it.

All good suggestions; and perhaps use a fluid with a higher boiling point. I prefer to bead blast my rotors when refinishing (and I recommend this to anyone when changing pad compounds), but I realise that's not practical for everyone. These work pretty well also: http://www.brushresearch.com/brushes.php?c1=6 (medium grit).

Change the pads to, they are probably cooked