The rules say one foot has to be on the floor at all times in non-lift dancing. Laura has one working foot. Easy.
A rumba on one leg might be all right, lots of arms and hips and very smooth so no jolting the ankle, male dancer often takes the female dancer's weight to hold her in position.
It would be awkward if she did leave, can't have 2 in the final, can't bring back someone who's already been voted out (well you could but there would be complaints), bringing back Will would be even worse, can't bring in someone new as they would be so far behind everyone else and they'd need a massive fanbase to have a chance of not being voted out first chance we get
But Laura's health is the important thing and can't see the producers trying to push her into it after letting Anastacia off the dance off.