There are no fights in the Source Temple (trials are optional) and the lava won't kill you. You need to speak to the wizard at the end of it to trigger the finale. Few fears on the random 1-shots from earlier in the game killing you by this point as there are no mines, BS fights to do that...if you are still hesitant (and who wouldn't be on the chance of losing 20+ hours of playing for a 1-shot)....simply leave 1 of your 2 characters in a safe place and complete the necessary stuff to trigger it. At level 20 the finale should be a cakewalk as no one in any of the fights can deal any serious damage.....the difficulty in the beginning is not, in any way, matched in the later 1/2 of the game.
