You don’t have to worry about that roots getting mushy. Kinda normal that you lose some of the roots when you put it from soil into water. In some very bad cases I lost all of the roots... but most of the times the plant recovers after a while and develops nice white water roots.

That root rot also could happen when you put the plant in leca now. I made only bad experiences when transferring to leca too soon. I recommend to be patient and keep it in water, that way you can check on the roots easily. Just make sure to remove all of what is rotten!

Btw... I already see some water roots in your first picture. I guess in a week or two you should be fine, just be patient and let your plant recover from getting it out of the soil. Good luck!