I've heard that Ketu in the 12th House signifies Moksha, and the possibility that this life might be the last one. Is it really so? What other factors are to be taken into account? I also have Saturn with Ketu in my 12th House. Would that be a hindrance?
Check whether this Ketu has got an aspect from Jupiter. if there is any, then, this may be the last birth.
8th house indicates time of death or total life span.
12th house indicates soul's interested path/journey after death.
if Ketu is in 12 with an aspect from Jupiter, then soul never likes to reincarnate again, and travels to supreme soul.
According to Jaimini, you will have to check your Karakamsha which is the sign occupied by Atmakaraka in your D9 chart. If 12th house from the Karakamsha happens to be in the sign of Aries or Saggitarius along with Ketu, one gets Moksha.
If Karakamsha is Mesha or Dhanus with benefics there, the subject gets moksha. If Mesha or Dhanus happens to be the 12th from Karakamsha and Kethu is there the person will get Moksha.
Adhaye 1, Pada 1. Sutra 70