I bought my dress off the peg at a discount as it was shop soiled. I had it dry cleaned and it has returned with some beads missing and a stain which they think may be a solvent stain. They have offered to re-clean it, this will mean that more beads come off - not something I am at all happy about. All they are offering me is £20 off the cleaning cost!
Most dry cleaners will have a disclaimer hanging in their store that covers them when cleaning delicate items such as wedding dresses. Things like beads coming off will most definitely be covered. Did you have to sign any sort of form before you gave the dress to them?
One thing that I can recommend is that you get some free legal advice about what to do next, (to have the dress re-cleaned or not and who should pay for it?) If you don't have a family lawyer, you can ask for advice at the address below, lawyers on line.
It might also be worth telephoning the Citizens Advice Bureau.
When it comes to the actual dress, I would be tempted not to have it cleaned again, depending obviously on how large the stain is.