This sink hole was never remediated and there are no visible signs of cracks, settling, etc.

This is much more stringent with FHA and VA loans with the property appraisal and condition report, they will require the deficiency to be remediated prior to closing.  

Under a co-tenancy clause, a tenant may have the ability to exercise specific remedies if the property’s occupancy drops below a certain percentage or if an anchor tenant is no longer operating at the center.

As far as rehab estimate of $30K-- a new roof, 2 water heaters, mold remediation, and a punchlist of little fixes (ex: rehang doors)-- there won't be much budget left for anything else (especially if the foundation does in fact need work).

High bidder’s remedy when sale is voided?

Refer to the bylaws, there should be a remedy and due process for enforcement outlined within them.

I would clear out the house and cover mold remediation beforehand.

The court held that after the debtor filed for chapter 7 bankruptcy, the servicer’s sole remedy to collect on the original note was to foreclose on the property—a servicer may not demand payment or remuneration as to the note.

If water gets into campers it can be difficult to remediate.

Unfortunately, you will have to remedy this situation now.