Scenario: My opponent attacks with five creatures, I block with Boros Reckoner, the combat damage he dealt is enough to finish me off but the damage I redirect via Reckoner would also reduce his life to 0, would that be a draw?
No, you lose, your opponent wins. This is because the Reckoner has a triggered ability, which has to be put on the stack and resolve for damage to be dealt to your opponent. But triggers are put on the stack after state based actions have been checked, and one of those is a player losing for having 0 or less life. So you lose before your trigger even makes it to the stack.
Scenario: My opponent attacks with five creatures, I block with Boros Reckoner, the combat damage he dealt is enough to finish me off but the damage I redirect via Reckoner would also reduce his life to 0, would that be a draw?
Shu Yun, the Silent Tempest WUR Voltron Control
Temmet, Vizier of Naktamun WU Unblockable Mirror Trickery
Ra's al Ghul (Sidar Kondo) and Face-Down Ninjas
Brudiclad, Token Engineer
Vaevictis (VV2) the Dire Lantern
Rona, Disciple of Gix
Tiana the Auror
Hallar
Ulrich the Politician
Zur the Rebel
Scorpion, Locust, Scarab, Egyptian Gods
O-Kagachi, Mathas, Mairsil
"Non-Tribal" Tribal Generals, Eggs
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)
Shu Yun, the Silent Tempest WUR Voltron Control
Temmet, Vizier of Naktamun WU Unblockable Mirror Trickery
Ra's al Ghul (Sidar Kondo) and Face-Down Ninjas
Brudiclad, Token Engineer
Vaevictis (VV2) the Dire Lantern
Rona, Disciple of Gix
Tiana the Auror
Hallar
Ulrich the Politician
Zur the Rebel
Scorpion, Locust, Scarab, Egyptian Gods
O-Kagachi, Mathas, Mairsil
"Non-Tribal" Tribal Generals, Eggs