If Bedivere attacks and deals 240 damage, Lyde has 571 health. Bedivere's Accuracy is 105.
Yukimura's Accuracy is 137.
Yukimura, depending on the number of successful attacks, can deal 0 (0 attacks), 349 (1*75% attack), 466 (1*100%), 698 (2*75%), 815 (75% + 100%), 932 (2*100%), well, obviously more.
With Bedivere, two successful hits of any kind are enough, but not just one.
Without Bedivere, only 75% + 100% or more is possible.
If we include the Guard in the equation... well, the damage is 165. With Bedivere hitting and the Guard hitting (which doesn't seem very likely, but is possible), Lyde will have 406 health left, and Yukimura will need to hit successfully just once (at 100%). So, maybe it makes sense for the Guards to shoot (I'm not even considering the option that both Guards will hit, but one of the two can, if both shoot).
For now, I'd stick to this option – even if the bartender is an additional threat.
Although, on the other hand, the Captain will now lock down Lyde, if I understand correctly, and we'll have another cast from Liviah... We can try without the Guard.