Ruby Weapon's Whirlsand--functions like eject?

Solution 1:

As you've already discovered, party members removed from battle by Whirlsand count as dead, unlike the Midgar Zolom's tail whip which counts them as escaped. It's unknown whether this was an oversight or a deliberate design choice by the developers, but considering that Ruby and Emerald weapons are meant to be the hardest fights in the game by a wide margin, it was probably deliberate. It is effectively an automatic kill that does not permit any sort of resurrection, nor automatic reactions like Final Attack.

Ruby Weapon does not like 3-on-1 odds, and if you try fighting it with three characters, it will Whirlsand away two of them at random near the start of the battle. Your best bet for taking it on is to load down one character with your best materia and equipment, then kill the other two before you attack Ruby; as long as you don't revive them, it won't bother using Whirlsand, and will fight the remaining character one on one.

(If you do this, it is strongly recommended that you use the Final Attack + Life materia combination; Final Attack + Phoenix is normally a better choice, but that will revive your entire party, at which point Ruby will take offense and start using Whirlsand again.)