The answer to your question depends on the wording of your declaration of condominium and the parametric boundries of your condominium unit. The answer is probably that the unit with the leak, the condominium association, and you all bear some share of the responsibility for the mold cleanup costs. You should contact an experienced real estate lawyer in yoru area to help you sort out the situation.
Disclaimer: This answer is provided for informational purposes only, does not constitute legal advice, and does not create an attorney-client relationship. Actual legal advice can only be provided after completing a comprehensive consultation in which all of the relevant facts are discussed and reviewed.
This is most likely your condo associations responsibility to investigate and resolve. If you have not reported this to your association, you should report this situation as soon as possible. the fact that the neighboring unit where the problem is most prominent is is foreclosure may make getting access difficult and you're association may have to force their way in to remedy the problem. This answer is based on the assumption that you live in a condominium association where the owners own the air space and the walls, ceiling etc are part of the common area. And the very first thing that needs to be determined is the source of the water that caused the mold to develop. And unfortunately, most mold claims are excluded from insurance coverage.
This response should not be considered legal advice nor do we have an attorney-client relationship. Legal disclaimer: The information presented here is general in nature and is not intended, nor should be construed, as legal advice. This posting does not create any attorney-client relationship with the author (who is only admitted to practice law in the State of California). For specific advice about your particular situation, consult your own attorney.
It does depend on the contents of the governing documents of your association as to who is liable. This can be tricky because unless they state the association was organized pursuant to Florida Statute 718 "as amended from time to time," new statutes cannot be applied retroactively to change the contract. Only new procedural statutes or statutes passed as a public policy would apply.
FS 718 does require unit owners to have their own insurance to cover the walls, ceilings and flooring, among other things, of their units and to provide the association with a copy of the declarations page of their policy.
An adjacent wall is most likely a "limited common element" or "limited common area" if it is shared with the adjacent unit. Also, if the pipe that was leaking serviced more than one unit, then that pipe is a limited common element the association is responsible for repairing. However, depending on the documents the association may or may not be liable for repairing the walls. Many condo documents provide the association is only liable for the exterior wall and any shared elements for plumbing and electricity. Older documents may require the association to replace the sheetrock, but not paint it.
If the leak was caused from negligence of the unit owner and the pipe services just that unit, the condo association is most likely not liable and you would have a claim against the other unit owner, who is obviously not around. You may still be able to file a claim against the unit owner and the unit.
You should consult with a condo lawyer to interpret your documents for you and determine if the association is liable for any of the repairs and if it's feasible to file a claim for damages.
This communication is not intended to create an attorney/client relationship. It is always recommended you consult an attorney in person to discuss your case. The Law Offices of Stage & Associates practices state-wide and represents homeowners and community associations. Please visit our website at www.stagelaw.com.