I'm slightly surprised BA saw the injunction through: to an extent, I think they blinked. Had the strike gone ahead BA would have enjoyed massive public support, and had they wanted to play the hardest of ball could have simply shut down the airline on the first day of the strike and waited for the unions to rip themselves to pieces (in effect, a lock out). That they didn't want to try this line implies that they don't have the money or nerve for a full-scale battle.
On the other hand, the unions blinked too, perhaps having realised the enormity of what they'd let themselves in for. They could appeal the ruling, which they don't seem to want to, and this judgement gives them the moral fire in their bellies of ordering the strike without actually having to see it through.
If I were Walsh, though, I'd be hoping that some cabin crew are foolish enough to stage a mass sickie. Because then I can sack them on the spot, replace them, and take some hardcore out of the re-ballot. I'd probably lose a few tribunals six months down the line, but it'd be worth it. I don't know either if he has the nerve or the cabin crew the excessive bravery to go down this route, but it would make for tense viewing for other trade unions.