So, in Unremembered Empire, Guilliman is caught in partial ceremonial plate and unarmed against a 10 man Alpha marine Killteam. He lives, barely, so I'm a little curious how the mathhammer would play out on this.

Assumptions for this case... treating the Alpha marines as 2 5 man Veteran Tactical Squads from the HH book. They get to go first, 1 has a power sword. This is consistent with the load out they had in the book. I'm giving them the first turn too. I'm taking furious charge as both squad's SR and we're just going to ignore challenges (as they didn't seem to factor into the fight). I'm also giving them preferred enemy, as that seems a reasonable boost for this "to kill a primarch" kill team

For Guilliman, I'm giving him a "standard" stat line for a primarch

WS7, BS6, S6, T6, W6, I6, A5, LD 10... but no special equipment and just a 4+ save (seems to fit what the armour would have been, shoulder pads, chest-plate, greaves, but no helmet, only one glove, does not seem to have been power armour).

I'd give Guilliman cover saves, but doesn't really matter. I'm also not playing out the fight exactly like it happened, just seeing, given the basic set up, if it should have been as close a fight as it seems.

So, first round, the squads open up... that's 5 rapid fire bolters and 5 pistol shots (charging into CC), 15 shots, 13 hits, 1.3 wounds (so we'll say 1... Guilliman down to 5). One of the squads charges... Guilliman gets hit 5 attacks, 3 hit, doing 1 wound (locked in combat with 4). Those 4 get their 4 attacks each, 16 attacks, 9 hits, 1.9 wounds (Guilliman down to 3). Guilliman fails IWND, on their turn he attacks again, killing 1 (locked with 3). They've lost their charge bonus and FC. .6 wounds, but we'll give Guilliman a break since I rounded up to 2 wounds last time. His turn, kills one (locked with 2) and fails IWND, and then on their turn kills one (locked with 1), then on his turn kills the last one. He's due to take a wound, put also passes IWND and has to face the last squad with 3 wounds left.

So to stop the process... he'll pass one more IWND, but they have a PS and can shoot before charging. Basically the book was right on. This one comes right down to wire. The book lets Guilliman loot bodies as he goes, so that's the only reason he should live.

Well done Abnett and FW... book follows rules